Easy there, Debbie downer. Look at the QBs he's had to work with in new york.
One of them was mark sanchez. He went to the playoffs with him. Twice. The same guy who looked no better this year under an "offensive guru" who I'm sure you, and most of the board, would have creamed their shorts over had he been hired instead of Rex.
Truth is, the bills offense is probably going to suck again next year unless they get lucky at the QB position. And no hot shot offensive coordinator flavour of the week would have been able to do anything about it.