Boost. Light Speed Dash. Blue Tornado. Axe Kick. Stomp. Bounce. Fire Somersault. Slide. Sonic Wind. Drop Dash. Elemental Shields. Peel-Out. Insta Shield. I could keep going but I think you get my point-there's a lot of abilities Sonic could use in Smash. They may be circumstantial in some cases (like Sonic Wind) but that doesn't matter, it can still be used as inspiration for a move in Smash. None of these require outside assistance, at least to my knowledge. And telling me Boost can be simulated with a Run Impact spirit is like telling me Bomberman is already in Smash because you can play his Mii Costume and use X Bombs only.
That's just his fights with bosses. If that were the case, Mario would be a campy character too because many of his boss battles are essentially the same thing. It would be more accurate to his home series if Sonic's playstyle didn't have a move that made the game slow to a halt-that's not Sonic's style. He should still have the Spindash of course, but it should be nerfed or altered in a way where his entire playstyle doesn't revolve around it. The whole thing about Sonic games is knowing a level and blasting through it as fast as you can. I don't know how they could make that work, but if they made Steve feel natural in Smash they can surely do it for anyone.
- Light Speed Dash: requires a trail of Rings, and unlike Pac-Man, Sonic isn't characterized in Smash as an arcade themed reality warper. The one exception in his spring is probably a necessary one as he would not have a vertical recovery otherwise.
- Blue Tornado: Possible if we look at the Sonic Heroes version, but wouldn't a stationary trap make Sonic campier than he already is?
- Stomp: his current down air is pretty much the same thing. Ditto with Insta-Shield and Nair or Fire Somersault and dash attack; if anything the fire would just be a hindrance against Blast Boxes or TNT.
- Drop Dash: Superfluous when Spin Dash and Charge can already be used in the air in Smash. In fact, would you not say these versions are the precursor to that?
- Elemental Shields: Pokemon Trainer in Brawl proved why elemental matchups are bad, when some characters reliant on one could be unreasonably screwed over by one. If you just mean the moves they grant, the fire one could be a reasonable alternative, but it could also unintentionally remove one of Sonic's current main weaknesses, a so-so disadvantage.
- Peel-Out: This move is only necessary due to Sonic games relying on momentum. Such a thing would be painfully clunky in a fighting game, so it's better that Sonic can instantaneously reach max running speed.
Really, none of these moves would significantly alter Sonic's current playstyle, even in best case scenarios where they're not just aesthetic changes. As long as Sonic remains the fastest character in the game by a significant margin, hitting and running is always going to be the best option in protracted engagements that simply cannot reflect normal Sonic level gameplay. I'm sure you can tear through stuff like Subspace Emissary levels the way you could Sonic levels though; that's probably a reason you get him last there.
