I feel like

more than anything was just Sakurai trying to bring in another "surprise character" but couldn't think of another important enough historical character like

, so he just settled on a Mario mook as the surprise this time.
If there's anything I think Plant killed, it's the notion of every Smash game having some random 80s character every game. I'd honestly go as far to say that Mach Rider to me was low key one of the red flags regarding the validity of the Grinch Leak, because well, it'd feels like whoever made the banner was oeperating on the typical Smash fan logic of "well, got to have a retro character this time!".
I legitimately think

were the only characters in Smash included for the sole purpose of including a random NES era character; Sakurai even claimed that he cycled through various other options for the slot like Urban Champion, Bubbles, Excitebiker, etc but ultimately settled on the Climbers because he liked their gimmick (the duo fighter thing loosely inspired by the original game's co-op mode, obv) the most. As mentioned above, the likes of

are technically from that era too, but Sakurai would sooner describe them as "surprise characters", and he considers Plant to be Ultimate's equivalent, thus once again kinda killing the notion that there has to be an dusty old 80s character every game.
So I guess that leaves just

, who on the surface level just seems to be another random NES/Famicom (technically Famicom Disk System in this case, uh-huh) era character like the ICs, but Sakurai has actually implied in the past that Pit's inclusion was based on his popularity.
I feel like to some extent, people kinda forget that before Uprising, there was a genuine amount of interest for Pit's return and a thus new Kid Icarus game. Go back to discussion regarding Melee circa 2001 and you can already see a handful of people requesting or speculating for Pit to make it in, such as, for example:
https://themushroomkingdom.net/board/index.php?topic=1013.0
Or how about this old article:
http://web.archive.org/web/20020202070514/http://cube.ign.com/news/35351.html
Heck, even Pit's English trophy description in Melee infamously ended with "Will Pit ever fight again?".
Sakurai himself even stated that one of the big reasons he went with the Kid Icarus license when putting together Uprising, was once again because he aware of demand for a new game in the series, especially after Pit's appearance in Brawl.
So personally I don't think Pit's inclusion was as arbitrary as some people seem to think it is, it just seems like Sakurai wanted to fulfill a fan request who happened to be old/forgotten, kinda like Brawl's equivalent to Smash Ultimate's King K. Rool and Banjo-Kazooie if anything. I don't think any of the other weirdo NES era characters were ever on his level.