This.
Having a defensive minded HC is fine. The problem is McDermott's defenses feast on the mediocre to bad QBs (of which there are many in this league) but get eaten alive by the good QBs.
Thus, in close games (which are typically close because we're playing a good team) coaching becomes key. It's good enough to win a lot of games but not good enough to beat the best.
McDermott is a good, but not great, HC in my opinion. Saying "you could do a lot worse" means nothing.
You could do a lot worse than Doug Marrone, obviously.
You could do a lot worse than Dick Jauron (he was coach of the year once in Chicago and went 13-3 in the greatest turnaround in team history)
You could do a lot worse than Chan Gailey, whose teams were fun here and there and even beat the Brady version of NE once or twice
That argument means nothing, really. Also, how different from McDermott would the above coaches' W/L record be with Josh Allen?
Put another way: if McDermott got fired and some other team (likely without a top QB) hired him, how do you think he would do?
All of this is a moot point, because ownership loves him, so we're going to have to overcome coaching to win a Super Bowl.