I take it Meta Knight, Cloud, Sheik, Link, Lucario, and Samus are characters you use. What I'd like for you to do is the next time you have your Wii U on, go to Vault and check Records to see who you play as the most. Then see who is the second most used character. Focus on those two. If MK is the character you use the most, and if the second character is a character you would not use as a secondary, find a secondary character who you like and feels right for you. Focus on those two characters. When you have too many characters to play as, you spend less time on each one. Or, perhaps you spend most time on one and neglect everyone else. Also, feel free to read from the link in my profile.
I did just delete my data on my old Nametag a few months ago, because before it wasn't too uncommon to hit "random" because I still had fun playing the game casually for a while. Recently I've been trying hard to improve like never before. So the data pretty much isn't there. So I have to rely on the system's stats instead of name tag. Since I'm basically the only one that ever plays, that should be accurate enough right?
Results for battles is:
699

Meta Knight - I did force myself to get better with him after all. So a high amount of matches is to be expected. Of course, I wouldn't be too surprised to see a bunch of people here have matches in the thousands. Probably around 50-100 of these matches are fighting a friend who is a Pikachu main. Which did help me discover that I have a bad habit of not baiting dash attack/grab and doing something else. Also that I sometimes default to panic shielding. In For Glory, people usually don't have time to learn that I dash attack/grab without ever baiting it, so once I played a friend for that long, it felt extremely weird to finally get punished for that because Meta Knight's dash attack/grab is pretty darn good compared to most characters.
458

Link - Learned Smash off him in Melee, so I did default to him for a while. It was rare to for him to lose... However, I haven't used him much since I got my lan adapter. Now I'm wondering if I was winning cause of random lag, or if I've slowly gotten worse with Link because I'm more used to Meta Knight now, or if I just ran into a big bunch of good players, because I was losing for a bit recently with Link since I got my Lan Adapter. Then again, I've only swapped to Link when someone was kicking my butt in the first place, so there's that too.... I sometimes like to swap characters to see if I can find a weakness in someone's playstyle, and then swap back to the other character and try to imittate it with my previous character.
221

Samus - Samus in Sm4sh feels like the best version of her so far. So I played her a lot, and I used to default to her whenever I'm not feelin Link or Meta Knight. Also, I love swapping to Samus when someone plays Fox/Falco. They always lose because they focus too hard on reflecting my charge shot.
209

Ganondorf - Few reasons for this guy. Sometimes I use him so I can train my brain to not be so aggressive, because it's not really a thing you can do often with Ganondorf because he's so slow. Also it's for when I get frustrated when losing with my other characters, and want to have a simple character to absolutely wreck the opponent with and it clears my head up faster than taking a break from the game. I don't know why, but a lot of people don't seem to know how to fight Ganondorf properly. Of course, I have a hard time refusing a Ganondorf ditto.... I mean I love dittos in general, but Ganondorf dittos make me even happier.
143

Shulk - Surprised I have so many matches with him. I bet a bunch are when Sm4sh was new and I was trying to get used to him. I honestly don't know if I'm good or not with Shulk (I just know I'm not amazing). I do seem to do somewhat well with him though. Putting off playing Shulk in Smash 4 now, waiting for Smash 5 because the selecting of Monado Arts was my biggest problem with Shulk because it would take me out of the game.
141

Cloud - Easiest character I've ever played in any smash game. I usually end up winning with him and his advent children outfit looks cool. He doesn't feel very complex compared to many characters either so I didn't play him as frequently because I felt like playing more matches with him wouldn't effect much. My friends don't know how to deal with Cloud, and a lot of For Glory players don't either. I can only imagine how much easier Cloud would be if I could short hop easily and master his frame cancels. Clouds biggest problem for me is that I don't have the nostalgia and love for Cloud like I do with other characters, so it's hard to find the drive to play with him.

Marth suffers from this too, but Marth's case is a bit more extreme since I don't care about Marth as a character at all (aside from the cool cape and flashy sword which is just appearance). Marth feels pretty perfect gameplay-wise.
115

Charizard - Once upon a time I wanted to try maining Charizard. Though as time moved on I realized that he never really gets more complex due to the end lag on his moves and just the way his moves are. Even when looking at top level players, he looked so basic and predictable. Easy to do well with Charizard at least, I just didn't see much room for improvement with him.
103

Little Mac - I love underdog characters, and Little mac is so friggin fast. Of course watching Sol play Little Mac is a big reason. Especially watching him fight some Toon Link and watching his patience to find a time to push through the barrage of projectiles was so cool.
https://www.youtube.com/watch?v=cdLnGJRv08g I doubt this is his best performance, but the pace of the battle is a lot different from what I saw in most smash battles I see. Another reason why I play Little Mac is that I used to have a tendency to want to jump into the air constantly, so playing a character all about being on the ground was a drastic change of pace and actually got me to learn how to be more smart on the ground with other characters as well. Also, I love playing Little Mac because people don't expect him to be good, kind of like Ganondorf, but not as well known for it like Ganondorf is. If I never saw Sol play Little Mac, I probably would never have thought about playing Little Mac competitively.
91

Lucario - All the way down here...... Like I said earlier, I love the character a lot despite him rivaling Meta Knight for being favorite on the roster, I just never had an urge to play him. I put 15-20 matches on him last night because this month I was going to try to get a lot better with him. I was horrible with him before. However watching Tsu play him, and Izaw's guide on Lucario, I improved drastically compared to the previous times I played Lucario and I'm really digging his style. I never felt like I was in a losing battle... Well except against some extremely skilled Mewtwo player. I think that was the second time in my entire time of playing smash where I've been wrecked so hard that I didn't even touch the enemy before I lost a stock. Mewtwo is just so much faster, longer range attacks, and you can't use aura sphere as easily against him as with most characters because of a reflector and his own projectile. Of course, he also kills lucario early because of his glass canony nature. If I ever try to get amazing with Lucario, that's a matchup I'll have to learn for sure.
68

Kirby - 10th place..... Safe to say Kirby and everyone bellow him don't get played much at all. There's a couple times I wanted to get good with him because that copy gimmick is very interesting to me and would force me to look more into certain match ups more often.
61

Zelda - Probably all of these matches are from last month when I was trying to get good with Zelda. Never used her much in Brawl or Melee (cause sheik), and my niece wanted to main Zelda so I gave it a shot so I could give better advice to her. I feel like I need more time with her to really know though if I like Zelda or not. I just love that a good Zelda (which is hard to find), is incredibly scary, and that interests me.
60

Mii Fighter Swordsman - I wonder how many of these are against cpus compared to vs friends. I love the mii fighters so much because their movesets look awesome (they were made specifically for smash of course). Of course, lack of being able to play them on For Glory, and finding out that tournament rules on them are never the same really made it impossible to want to main them. Hoping they are playable online in Smash 5, because they are really fun.
Apparently I've only done 40 matches with

Sheik (ranked 19th), probably all from that month I was practicing Sheik. I really really want to do more matches with Sheik because she's so darn fun and every match feels different..I do feel like not all battles are shown however, because

Bowser Jr only has 2 matches on him. I know for sure that I definitely played more than 2 matches with him because I was very curious about that character at one point and I definitely remember playing at least the Bowser jr, Lemmy, and Roy skins.
Looking at how low the amount of battles there are on some characters, it makes me wonder. How many battles should you do with a character/all characters before you say that you will probably never/probably not main/secondary them?
On a side note. Really loved that essay you linked in your signature btw. All that stuff you said in there is kind of stuff I tell other people in other games all the time when they are learning a game. Nice to see someone else saying it. Only piece of advice in it that I never really follow whenever someone tells me it, is to reward yourself after getting something done. That has never worked for me in my life because I will go "why wait till after the reward when I could have it now?". Also since I've been eating a lot healthier now, I don't even have a food reward system, so I don't even know what I could use as a reward. I mean video games are basically my reward for tough stuff in life though, but trying to reward myself within a video game, I have no idea what I could do to reward completing some annoying task (like short hopping for hours... I really hate that).
So here’s an idea: go on for glory and try winning a match as Marth, Mario or Captain Falcon while only short-hopping.
You’re probably thinking, “that’s a terrible idea,” and it kind of is. I just think you need to get the muscle memory down. Short hopping is hard -and I know you’re giving it your all but I think practice makes perfect.
Why those three characters? Well in my opinion, they’re the best “fundamentals” characters in the game. If you learn them, you’ve learned the game. They also have good aerial attacks so that’s important. Feel free to use whoever though because I’m just some random guy on the internet.

Mario short hopping..... I'll save that for when I want to get better at short hop reverse back air fast falls. I'll give Marth and Captain Falcon a short. I miss playing

Marth, so that should be interesting.

Captain Falcon.... I've never really played seriously. I generally just try to see how many people I can beat with only falcon punching (and I get away with it too often in for glory.) I only know a few things about captain falcon so I'll give it a shot. I'm usually inclined to not be afraid of captain falcon. He may look intimidating with his speed and have some nasty combos, but opponents using him always seem to struggle KOing me with him. I'll give it a shot though, since if I can win with just spamming falcon punch, I can probably win trying to get better with short hopping.... assuming I can even short hop with Captain Falcon. He's 5 frames so that should be a bit easier than Meta Knight, but not too easy like it is with Link/Ganondorf.
As for the videos you've posted:
Ah Izaw's training session with

Oblivious Loser. I have both of those videos on a playlist, and I sometimes just leave those videos on in my house when I'm doing stuff so when I take a break from doing whatever I'll look up and see them fighting. Also Oblivious Loser's 2nd video, he's so much better and it's a bit inspiring. Also helpful that Oblivious Loser is one of the people I like the most out of the people Izaw has trained, so it's very easy to just listen to them talk. Izaw's training session videos are very nice. Haven't watched them all of course, but ocassionally there will be some specific tips that pop up that I never see anywhere else and helps me use all my characters better. It's random stuff that you can't really just search for and find.... Since I love listening to Izaw's training sessions, perhaps I'll write down all the tips and time stamp them and post it somewhere someday.
Izaw's

Link in Brawl made me get interested in competitive Smash because I loved the

Link vs

Snake (Calzorz) offline friendlies matches so much (before, I either didn't really care for it, or didn't like it because of other competitive scenes in games being so toxic. So I never even though about whether it'd be fun to be competitive or not in Smash).
https://www.youtube.com/watch?v=SiNu0dqERIQ This first video has a dumb annotation at the beginning. just click the X.
https://www.youtube.com/watch?v=0NppxHEtrTw Since I learned Smash with Link, I looked for Link videos and Izaw popped up. I loved seeing how many trap-like projectiles were being tossed out in the Link + Snake matchup because it's a lot more interesting compared to most fighters. Izaw always had a very flashy Link that is so fun to watch. Some of his matches with


Haze were good too. Though, he definitely has improved at the game a bit since these videos... I mean, kinda obvious, almost 10 years since these were uploaded. His Smash 4 Link's gameplay is much different from his Brawl Link's playstyle, but it's still pretty flashy.
Ah smash corner's meta knight video. I've seen that plenty of times. However it was made before the final patch, and if I remember right some things do not work quite as well anymore because the up air got nerfed since that video was made. However, I never got around to taking notes about which specific things still work and which ones don't..... Also that video is a constant reminder that I need to do reverse short hop back air fast falls with Meta Knight because that jab lock combo is so nice.
Maybe I'm just spoiled by watching other Meta Knights, but Zero really makes a ton of small mistakes in that Meta Knight For Glory. It's really funny to me. He must be too distracted by trying to explain things. 12:30 "see how jab is amazing, you can just hold it there" and immediately gets down aired because the end lag on jab is really bad. I'll watch the rest of the video later (probably with dinner), but just hopping around, he seems to be really struggling to use Meta Knight compared to other characters. Which is strange because I have seen Zero use Meta Knight well sometimes in some other videos (or maybe I was so bad before that I didn't see the problems with his Meta Knight). I will try to take some notes though. Forward Smash is a move I neglect a lot, because it's just so unsafe if the opponent knows when you're going to use it and it's very easy to punish a Meta Knight that doesn't use Forward Smash correctly since it locks him in place making him incredibly vulnerable from above. I have made a couple Meta Knights stop using Forward Smash, and it makes me smile everytime I make a Meta Knight stop forward smashing. :3
Then a match with MK Leo. Ah so much better than watching Zero play with him. The control over the character is so beautiful and I love to watch it. I need to look at some Tyrant and Abadango Meta Knight plays as well because I've gotten much better since the last time I saw their videos. So I should be able to understand why they did the things they do more now. All I remember is that there playstyles for Meta Knight were a bit different from each other. On a side note, I don't know anything about competitive peach gameplay. So it was a bit harder to know why MK was doing certain things just because I don't know

Peach, thus don't know what to avoid/take advantage of. I can't even remember the last time I saw someone play peach.