To preface, I'm by no means a Sonic main, and my Roy just got bodied in my last tournament by @
Solharath because I had no MU knowledge then, and he's just a much better player than me.
That being said, I don't think Sonic is A tier.
He has a good boost grab and can grab out of side-b, and he has good edgeguarding skills with his fair meteor and sometimes his cool dair spike. But Sonic has zero disjoints and very short range. Though he has high speed and a great dashdance, he's not actually much faster than Fox in any way that's meaningful, IIRC. His recovery is also not as good as people think it is. It's incredibly easy to edgeguard because you have such little air control after the upB, which doesn't really have a sweetspot, since his hangtime has no ledgegrab box, so WDing to the ledge to kill Sonic is simple.
Contrast to Ike. Ike has burst movement options that have more coverage+disjoint than Sonic in QD, out of which you can WD, grab, usmash, RAR, pivot grab, jump, or QD attack. He has massive disjoints and huge horizontal and vertical recovery, which can both be used in one recovery by walljumping out of QD. His recovery has similar range to Sonic's, but is much, much harder to edgeguard. It goes very high still, and he has a useful walljump, so he can often recover onstage if he has to. He can sweetspot, and the only way to ledgehog him is to grab edge just before he tosses his sword up and roll right before your invincibility runs out, because otherwise the tossed sword will hit you. If you don't have a disjoint, you'll probably struggle to hit him out of his upB no matter what. He also has chaingrabs and pseudo chaingrabs, DI mixup throws into kill/combo setups, a meteor/spike aerial, an armored spike in his nB, amazing offstage game granted by massive disjoints and good recovery, and kill options off the top. He has a jab combo that nets him a free grab. One of the best nairs in the game, probably.
I'm sure @
Solharath or someone could correct me on some of this, but I'm fairly sure Ike is much better than Sonic overall.