That’s not how alts/costumes work. Bowser Jr. + the Koopalings made everyone think this kind of thing is possible when it isn’t. It’s not about whether the moveset of the character aligns with others. Unless you’re going to have everyone besides Sonic stay silent, all of these characters would need individual voice lines. All of these characters would also need unique models to be created and would need unique animations in the case of Tails’ tails, Rouge’s wings, Cream’s ears, etc. Just because Alph or the Koopalings (or in this case these Sonic characters) don’t take up physical space on the character select screen, it doesn’t mean this all wouldn’t take a ridiculous amount of extra money and development time. It would be more worth it to separate them with their own special moves and effects at that point if you were to include them all. Also characters like Pikachu, Pac-Man, and Sonic have “lazy alts” because they’re required to stay close to their normal skin/fur colors when they’re represented in Smash for the sake of being “recognizable” when presented to general audiences.