I get that his numbers were horrific, but when I watched the most freely available plays from that game that I could find, I saw his WRs and OL completely outmatched. He'd make a back shoulder throw, and the CB would basically Moss his poor little WR. You could say that he shouldn't have made this throw. Fine, so what should he have done? If he can't trust his WRs in a one on one matchup, then he's reduced to midrange throws to gaps in zone over the middle, which Clemson wasn't playing I'd assume. So, he basically can't play within his offense and win that game. This all goes without mentioning Clemon's DL talent superiority.
I don't think it's always fair to point to a player's toughest opposition in college and say "that is proof they are/aren't ready for the NFL" because the talent disparity is too great. To take Newman's case again, I want a QB that is willing to take 1 on 1 chances with his top WR. If it's an INT, that's the WR's fault. We'll get him a better WR. (If he does it over an over again, maybe that's the QBs fault, but that's a different situation).
A different situation is Jordan Love. I saw him terrified for his life during the LSU game. Terrible mechanics, terrible decision making, lack of pocket presence and mechanics in the pocket. Adversity just broke him. In Newman's case, I just saw a guy on a team that was destined to lose to a far superior opponent.