i was not aware starfox was that popular, but i guess im just an old fogey who doesnt know what's hip
i still dont think fox, as a ship pilot with no previously demonstrable ability to fight on ground, self-combust, defy gravity or even jump, really deserved to be in a beat-em-up type game, and certainly not as the most acrobatic chracter in said game (falcon is an even worse example but we'll leave him out)
like, even in the GCN zelda-esque games, he didnt use his gun, he couldn't jump, his reflector didnt exist and his main weapon was a magic stick
kirby, with an arsenal of basic physical attacks, and more importantly the swallow gimmick, had every right to be in a colourful game like smash by virtue of the precedents for gameplay his previous titles set - the fact that he likely backdoored his fixed position due to sakurai detracts from his 'right' to be there, but in terms of gameplay he was always suited, definitely moreso than the pokemon, ness and the pilots, and arguably moreso than link