You have this exactly wrong: QB play is all about accuracy and moving the chains (throw and run). If the offense performs well it’s almost always the QB that is leading the way.
Every position on defense (including CB) is highly context dependent. Each player assumes a role in a scheme on each snap. A DB in proper zone position can appear to be “beat” if the other players don’t do their jobs. An example, was when the WFT let Hop go middle on his TD catch and LC didn’t man him up b/c he got caught staring in the backfield. The DB on the outside got “beat” but only because LC didn’t do his job.
Erm, no. PFF grade every play a QB makes. So every run he makes, every linebacker he reads on an RPO, the accuracy of every pass, how long he holds on to the ball, did he invite pressure, did he cause the sack, did he not see any open guy, is he throwing guys open or waiting to see if they become open and a hundred other things. It's even more complicated with a running QB.
By comparison, P2 on 99% of his snaps is in man coverage on one guy. We rarely play zone. He's rarely asked to rush the passer.
But, this point aside, what you are trying to say is that PFF got it wrong this time. That he was better than his 30 grade, but they got it right all the times he had an 80+ season. It's just a coincidence that most fans thought he had a bad game at the same time PFF thought he had a bad game and that PFF's grade line up pretty much with how everyone thinks other cornerbacks have performed. It's just P2 they are wrong on.