If the level of the QB matters, then every pro BB stat and comment should be starting with "But he had Brady....". And that's been a big part of the point of this exercise.
BB without Brady is a sub .500 head coach, yet people here are saying things like "But Payton had Brees"/"But Tomlin had Roethlisberger" as if that's supposed to be some magical reason that those coaches couldn't have down years. Brady just had his first losing season, because his head coach sat most of the team in much of the last game. But even Peyton and Montana had losing seasons after they'd had 13 win seasons, yet before they reached their NFL dotage (Granted, Montana's was in a shortened season, but he went 3-6).
And I don't point that out to belittle Belichick. I point that out to note that such context has to be taken into account, and that it's been a huge advantage for BB.