While Sonic is a lot better in this game (I don't consider him too far behind Rosalina, he's easily top 10 himself), his aerials still have a lot of landing lag if you use them too close to the ground, and his Smash attacks are SUPER punishable, though they are quite strong and useful. In general though, I prefer gimping/aerial chases when getting kills with Sonic, or playing mind games to get a Smash in, since he excels at those things.
His U-Tilt is definitely punishable too, though F-Tilt not so much because of it's range.