IMO "Pac-Man uses too much from other games" is only really a valid criticism under the expectation that a Mappy or Galaga character could be playable themselves, which I very much doubt, as cool as it'd be - Pac-Man's whole identity is "the old gaming guy", and on the side "Namco's mascot", he isn't losing any individuality from referencing other games because that individuality was lost mere years after his debut, he was "The Gaming Guy" in the 80s, and he's "The Old Gaming Guy" now (that's something I've noticed in general, a lot of Pac-Man fans seem to be a bit resentful towards Pac-Man being used as a nostalgia character, despite the fact that well... he is, and was long before World) - it makes perfect sense for him to represent old Namco games because those are his two mainstream identities, a vintage character and the face of Namco.
Mappy and Galaga are the only games that "lose out" on individuality in Pac's moveset, if any kind of Smash reference is a "loss", but Galaga is point blank unambigiously part of the Pac-Man universe circa World (in fact most of the Pac-Man cast is just recycled characters from non-Pac-Man games, Pooka is part of Pac-Man's family for instance, the same could be said for one of Pac's closest parallels, Mickey Mouse, who would often interact with the early Disney movie cast like Dumbo and Jiminy Cricket in the 50s/60s), and while Mappy's in-universe connection to Pac-Man is a bit looser and mostly through games that could be described as crossovers, the games are joined at the hip, being connected not only by their time period but also their ragtime and 40s chase cartoon influences within both aesthetics and gameplay - it comes off less to me like "giving Mario a Master Sword because he's Nintendo's mascot" and more "giving Mario the Poltergust in PSASBR because Luigi has a snowball's chance in hell". If playable Mappy, Goro, or Galaga spaceship in Smash becomes a possibility some day for whatever reason, we'll talk, but for now, this is the best it gets for Namco's misc. stuff, and shifting to a World based design would mean less games are shining bright, games that are more iconic than World, in a place where they otherwise can't.