No, he doesn't lag the game, but if you watch him run (or do other moves) it doesn't look like all of a proper run animation is present, like parts of his running animation are cut out, namely areas in between when he has his feet on the ground. So unlike the rest of the cast all of whom have nice "smooth" running animations, Wario's run looks kind of choppy as though he's skipping frames in his animation (saying he frame skips is just my way of defining how he moves). If I'm still not making sense to you go to training mode, slow the game's speed, zoom in on him and start running or attacking. It should make sense then.
Anyway getting back on topic. My friend has a bunch of hard core smash buddies that like to do tournaments in...New Orleans I think, and I don't think they've ever mentioned Sonic before. And out of all the people I know, some of which are into the whole tournament scene, only one person other than me plays as Sonic, and he plays as him so he can brag to other people about how he beat them as Sonic, so I'm pretty sure given everything else I've read on the boards that he's not a popular tournament choice.