It's not really that difficult. U-smash should NOT be one of the strongest smashes in the game, specially not when it has fuggin superarmor and lasts for like a million years. It also baffles me that he has a kill throw in b-throw. Those two at least should be nerfed hard. He already has a great recovery, which lets him go off-stage for kills and gimps, he should not have powerful ground attacks. Quick? Yeah, sure. Strong? What.
It's the same thing with Diddy. It's okay if he's fast and has dumb frame data. Quick characters are supposed to be like that. What quick characters aren't supposed to have is lethal weapons that kill as soon as some of the stuff the heavies have.
Why the hell is Sonic's u-smash so strong is something that still baffles my mind.