I feel Knuckles is probably the least divisive possible Smash pick, at least within the Western Smash community - like, would anybody actually object to Knuckles in Smash? I can see Adventure/Dark-era fans not wanting Tails because of "classic bias", or others not wanting Eggman because he's not a cool furry with a stylish 'tude or his similarities to Porky, but Knuckles is a character I don't think many people actively dislike and the only reason - valid or otherwise - I could imagine opposition to his inclusion is from first party devotees.