Belichick took a sh.tty franchise and was clearly in the process of turning them around when Modell screwed him and the city. Belichick drafted Brady and trained him to run their offense the way he wanted it run. And if you wanted to test your theory that it's all Brady all it would take is for Belichick to decide he was going free agent. He would last all of three seconds, would be the highest paid coach in the history of sports, would be given absolute control over all football operations, and there isn't a team in the league who wouldn't swap out their current coach and GM for him, so while you are entitled to your opinion of Belichick realize that's a lonely place too be.
You would however have triumph to keep you company, just make sure you get to the table first, from the looks of it he eats everything in sight.