Alright time to get cracking.
First of all, I believe ice climbers have the potential to be 2nd on the tier list when played right. The problem lies in the fact that there is no good ice climbers player atm.
My belief is that most ice climbers player are good with their characters, but are not that good overall at brawl. They have good "character skill" but not terribly good "player skill". This comes mostly from the fact that ice climbers have a huge learning curve character wise, and although at first it provides instant gratification when you learn to chaingrab/desynch properly, it does not necessarily allow you to learn how to be a smarter player. This is why when we saw the first outbreak of ice climbers, they were doing fairly good with lain almost beating m2k. Then people learned the matchup, and Ics started losing again because they were mostly relying on gimmicks at a basic level with not so good player skill.
Now, once you become smart enough, you learn that you can overcome most of these new problems by baiting mistakes from your opponents. The good side of ice climbers is that since they are 2, they can create more complex traps which make habits easier to bait, except that at first they were used purely as 1 shot gimmicks, not as baits. Pivot grabbing the tornado is a great example of this, once MK learns to space the nado too high for the pivot grab, you can actually simply crouch and upsmash/fsmash accordingly to the opponent's height after. In the event that they get hit while charging the smash, they get popped up directly above due to increased knockback.
Player wise, if you take a look at meep, prior to taking fox up, he was getting ***** by ally. He played fox for a while, went back to ics and took his first set from ally(some say ally had a day off, regardless of that, it shows alot of improvement). He explicitly told me that he had learned "to put others into incomfortable situations which allowed him to bait better than he used to prior to taking fox". This is obviously because his player skill grew because he was no longer relying on ics gimmicks, and could now land stuff he wouldn't before.
Character-wise, ice climbers have fairly good kill moves, a death grab, a good versatility due to their different ranges/speed mixups in moves, a great fear aura factor, disjointed hitboxes(hammers are really good in the air) and a unique desynch factor. On the bad side, they are gimpable, have slow air speed, bad walk speed, limited aerial abilities, nana is predictable(except when it involves certain moving platforms and certain random reversals) and grabs can be evaded if you do not make a mistake, and sopo is horrible on its own.
Now if we take a look at all of these, well most of these really are a non-issue once you learn to play them right.
Ice climbers are much less gimpable if you can mash side B fast enough, know how to recover using properly timed ice blocks/b-reversed ice blocks to use bair while recovering. Now your side-B allows you to keep your second jump even if you get hit, which is a huge bonus. The fact that ice climbers are not fast falls helps them recover alot since they can often simply DI up and recover because of their average floatiness. When you add clever use of Side-B/Up-B and footstooling, it makes gimping a non-issue.
Slow air speed is an inherent problem which really can't be changed -.-. On the other hand, their slow walk speed can be useful to quickly create mixups between walking and dashing to get in close range much faster than most would expect, same can be done through slow-dashing, but thats harder.
Limited aerial abilities would be quite honestly false, considering they have great comboability, that nair at low % sends down for a grab opportunity, and that fair is probably one of the best jump guard(see pierce's thread, he named it before me
)punisher ever since it gives the opportunity for a tech chase to grab. B-Air is very useful as a spacing move and is fairly lagless, D-Air allows you to quickly change your falling speed. They can desynch off any aerial in the hope of getting ice block to grab too, their aerial game is frankly quite good as all of their moves serves one of two purposes. Either they are easy to land and rack up damage/combo(upair/b-air), or they are used for landing grabs but are slightly harder to land(n-air and f-air).
Nana is a predictable dumb AI that will run into any F-Smash, amirite? Nope, wrong again. You can actually control's nana's AI from afar in order to create mixups so that its much harder for the opponent to kill her. You can go as far as control her DI, her movements, her jumps(depending on where you are in relation to her), keep her down when shes on the ground, keep her from killing herself due to input copies(I swear every ics run towards the ledge and shields when shes on the ledge....she lets go and airdodge). Due to all of these, it makes it much harder for the opponent to kill nana since you still have a decent amount of control on her. You can even pull of some crazy stunts to save her. For example, say Snake backthrows you offstage and hes about to kill nana with Fsmash. You know that even if you do an aerial you won't be able to catch her since you can't use an aerial until fairly late in hitstun. Well you could be holding R after an aerial in the air, and when nana will be sent towards you she will airdodge, then catch her with side-b. Ice climbers allow for a lot of creativity.
Now for grabs being evadable, I must say that imo this is completely false, ice climbers player skills are simply not high enough, all characters including MK have to land at some point, and you have ways to counter that. You can also beat rolls and spotdodges simply by grabbing at the right time. Often ice climbers simply miss some of those opportunities because they are not used to baiting such things. Even the tornado can be punished with a grab if done well, and it essentially becomes RPS on the type of nado hes going to use vs what punish your going for.
Finally, sopo does not suck at all. Yes, he has an under-average moveset, but he can still chaingrab for a long time most of the cast, heres a link to the list:
http://www.smashboards.com/showthread.php?t=246701 . Granted sopo is not fantastic on his own, he can still recover fairly well if you DI/footstool/side-b/b-reversal ice block at the right time. Due to his weird moveset, he can still use some weird traps to hit most characters. That his to say every of his moves in the air and on the ground get beaten by shield, except he can still blizzard/grab it for good damage, which still allows him to do some decent RPS battle vs the opponent. He also gains some decent baiting moves at mid-stock on other characters. For example when he D-Throws MK at 70%ish, he gets to follow up with up air if MK doesn't airdodge, but can still bait it to f-smash/upsmash.
In a nutshell, ice climbers are not placing so well because the character is so intricate, players are learning the character, not how to play brawl. On the other hands, top players like ally who can usually pickup a char with no problem still have to learn all of its intricacies before being really able to shine, which makes it a not so worthwhile investment for them and don't do as well as when picking up say falco or marth or MK. In order to have ice climbers at their full potential, you need someone who can play both at top level and know the character like the back of their hand, and so far it didn't happen. I think its doable, just terribly hard to reach that level but worth it, since ice climbers simply don't peak as early as other chars like snake.