If Sonic's moveset doesn't get an overhaul, then at least make his side and down specials different from each other and make him more expressive.
But they are different from each other. That's the point behind its design. They function differently while looking near identical so he can confuse the other players, since they don't know which move it is.
(Did you mean they're too similar regardless and dislike that? Albeit, the wording suggests they're identical, but I doubt that's what you actually meant, heh).
https://www.ssbwiki.com/Sonic_(SSBU) Quoted from here.
Spin Dash - Curls up into a ball, performs a short jump, and then starts rolling toward the opponent quickly. Holding the special button charges it up and increases its speed. In addition to granting 5 frames of intangibility after the charge is released, it boasts impressive combo potential, thanks to its ability to be followed up with any aerial attack. However, if uncharged, it stops when it hits a shield, making it very unsafe if shielded. When it is charged, however, the move is very safe on shield. It also boasts horizontal recovery potential when it is jump-canceled immediately upon releasing the special button; this turns the dash into a "Spin Shot", a quick, long-ranged short hop that can be performed either on the ground or in the air. Sonic can only hold the charge for two seconds when his Spin Dash is fully charged, but as the move can be jump-canceled, he can still charge it on the ground, cancel the charge with a jump and release it in the air while still keeping its charge.
Spin Charge - A Spin Dash that hits multiple times and has more momentum. It also has slightly different aesthetics compared to Spin Dash, and requires button mashing in order to charge. However, it lacks a short jump at its beginning, cannot be canceled in any way, and it can only become a "Spin Shot" when used in the air. Its charge can only be held for three seconds after Spin Charge is fully charged.
That said, this isn't saying it's done well or shouldn't be changed. Just that they are quite different at the end of the day. The custom moves in 4 do a better job at separating them, though, won't lie. Either way, I've been wanting a change too, but I'm well aware of its design choice. Generally, if a move is changed, it's not simply for balance alone, but sometimes it's that it fits the character overall better. Sonic being a fast and confusing guy still makes a ton of sense. Ganondorf getting his Flame Choke to replace Gerudo Dragon is a good example of using a move that fits his overall character. Other than Dark Dive, his special moves overall fit him. He's a brutal man who exerts extreme power and more. Dark Dive not being remotely changed(especially after Dark Fists actually fits him overall better) is odd, but hopefully they find something as a better Up B. Teleporting sounds good, but that's also a specific move where he does damage when he bumps into you, suggesting it should have a good damaging effect at the end only. Akin to Shiek's Up B, but reversed.