i agree, but I also think PFF actually takes into consideration of how the turn over took place.
IE WR ran off their route when the QB let go of the ball, or ball bounce off the chest of WR who was being held/mugged into a defenders hands, or being blindsided and helmet to helmet hit to cause a fumble.
They "PFF", also include turn over worthy plays in their grade, so if Allen threw a would be INT but the defender dropped it, then it would still hurt grade.
I think lol