McCarthy's problem when he gets to the NFL is that the passing windows are so much more tighter all the time than in college and he isn't going to have all day to throw like he did constantly at scUM.
He's fine when guys are running wide open and he has all day to throw, that's not how it works in the NFL a vast majority of the time though. When the pressure is on and coverages are tighter he turns into a pretty mediocre QB.
That and you have to wonder how much of his "success" at scUM was due to having a good idea of exactly what the defense was doing, because of their cheating of course not because he's some master student of the game defense reader.
Any team who would waste a 1st rounder on him is a special kinds of stupid.