No one player ever completely decides a game. A QB has a far more significant impact though. That's why it is good to look at exceptions in the context of a guy's whole body of work.
So it doesn't matter that your RS Jr QB could not move the O and get first downs or points vs GSU... who really couldn't defend anyone else for the rest of the year? You don't expect your RS Jr to play better than he did vs VU, IU, Bama, UF, etc? I do whether the name on the jersey is Guarantano, Manning, Bray, Maurer, or Suggs.