Can't argue too much about your comments, but I will say this:
The Bills threw a lot of different fronts and blitzes at Leftwich, most likely because he is a young QB and still has trouble with them. That appeared to be the case, as Leftwich appeared dazed and confused except for the final drive, when the Bills inexplicably stopped their previous ways. Gannon, on the other hand, has been around. He knows how to deal with blitzes, is able to move around in the pocket, and gets rid of the ball quickly and accurately. Gray probably didn't want to blitz and leave guys open, since Gannon could pick them out quickly.
That said, I still think Gray and the defense did a bang-up job against the Raiders. Sure, they made a mistake or two, but in the NFL you're going to make some. If we had any semblance of an offense, one or two defensive mistakes wouldn't be enough to lose a game like that.