It might have been the fan expectation going into the year but the quarterback is playing like the best player in football. If he maintains this level and they don’t progress forward from their usual standard, that’s failure.
It's almost like the lights out play of the offensive line and the balance Brady has brought to the offense has something to do with that.
You're discounting coaching to a ridiculous degree. What coaches do during the week is at least as and probably more important than their gameday duties (as long they hire good coordinators, which is also sorta part of the job). The most important trait of a head coach is to be a great leader. Andy Reid is first and foremost a great leader. Mike Tomlin is a great leader. So is McDermott. You want to build for the long term and put yourself into position to win every year.
But, to add on that, McDermott's actually been an above average, at worst, gameday coach this year. He was correct in going for it on 4th and 7 against KC, and no one else had been doing that. His 4th down call to go for it up 14-7 against Detroit had a much greater impact on win percentage than the 15-20 second difference calling timeout vs. not calling timeout would have had against the Rams.
There's a sect of fans who's just waiting for him to make a perceived mistake and uses that to shit all over a level of sustained success that arguably not even Levy's Bills enjoyed.