Fine I'll give my 2 cents on this topic.
In Smash 64, Kirby was a very good character, maybe too good in fact. People call Sakurai out for having "Kirby bias". Melee comes around and he nerfs Kirby HARD. Then there's Brawl, and then... Meta Knight happens, people say "Kirby bias" again. Smash 4 nerfs Meta Knight, and seemingly this time around... the "Kirby bias" talk SEEMS to have ceased... for now. Despite this, a few people notice how little represented modern Kirby games are. No stage, no remixes, only a couple trophies and Kirby's new Final Smash. These comments of modern Kirby representation are quiet though, and others ignore this aspect.
And now Ultimate. World of Light trailer shows Kirby being the only survivor to Galeem's attack for some reason. Cue "Kirby bias" once more. Game releases and Kirby fans inmedeatly notice how underwhelming modern game representation really is. Only a few spirits, NO remixes, while the old games like Dream Land/Adventure/Super Star get all this love. Meta Knight gets a DMK and Galacta Knight skin, and Dedede gets Masked Dedede as a Final Smash, but that's about it. KaTAM got a remix... and I can't forget about those Squeak Squad and Kirby 64 remixes in Brawl.. hey at least we got something.
To be frank, all this Kirby bias talk got me thinking... Maybe, and only MAYBE the reason Kirby representation is so polarizing is because of all those louder comments that have more to do with character viability, and the seemingly different meanings of the term "Kirby bias". Some people either say: "Oh this character is broken because Sakurai created it!" or "Why only Super Star? What about the newer Kirby games?". It's all over the place.
Sakurai sees these louder "broken character" comments and assesses them as a general term for the whole series. He doesn't want to make another Brawl Meta Knight making his characters balanced although low tier-ish, and he wants to get the quantity of Kirby content to a generous amount and in line with other series (even though mario pokemon and fire emblem get all that content, so it doesnt add up anyway lol). That would be fine and dandy, but Sakurai just decides to add more content from the games HE'S the most familiar with while the most modern games bite the dust. This seems to be the main problem.
Initially, I would just be like: "OK, that kind of sucks but he probably isn't too familiar with the newer games. He probably wants to give those games proper justice with representation, but since he's not familiar with those games, and is afraid to upset modern fans, so he just plays it safe, and adds content straight from those games, like their original music." But hang on... that just doesn't make sense does it? He has downright stated he played Three Houses before the final game released. That game is a long RPG, and Xenoblade 2 is a long RPG, and Persona 5 is a long RPG, and all of those games take a good while to beat each, so SURELY a 2D platformer like Kirby would only take him a few hours in comparison, right? It wouldn't take too much of his time, and are easier games to play and understand... right? He cares for his son's most recent adventures and new friends... RIGHT?
Well, after this tournament, and those anniversary tweets... yeah he does not care at all LMAO. Really, really sad, but I guess I should've expected it. It's honestly similar to how I feel about the Donkey Kong series' representation. Only the arcade games and DKC1. The other DK games barely get represented if at all. And the Wario series. And the F-Zero series. And even the Sonic series to a certain extent. And how StarTropics fans still have nothing... Yeah...
Hopefully in the next Smash game, things will turn around for Kirby and all those other series I mentioned. But I'm not holding out hope personally.