Quinto is a crappy actor, as is nearly everyone on Heroes. Even when it was ok the acting on that show was god-awful. Now thjat the show has turned to pretty much crap it's even more noticeable.
Which, whether I agree with you or not (I don't), is entirely besides the point. On Heroes, the actors do what they are paid to do - play the part they were cast for.
Welling, on the other hand, moans to the producers based on feedback on one episode.