Bill Belichick has won 43% of his games where Brady doesn't start.
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I see 21-23 with NE, 37-45 with Cleveland for 58-68 for 46%. Obviously there were some tough spots here, Cleveland was 3-13 the year before he took over. It was his first head coaching stint. Bulk of his losses with NE were in the first 18 games with Bledsoe. Team had some rebuilding to do after the end of the Carroll run. He's still 1 of the best coaches ever but the numbers aren't irrelevant either.
Just the idea he is worth more than QB's like Brady, Manning, Mahomes, Wilson was never true and unlikely to hold up as an opinion unless he got some really good short-term variance (which does happen in the NFL obviously)
But I'm just gonna go back to the point I made in the thread about other coaches and coaching in general, it is fucking hard. The NFL is designed for mean regression and fragility. Elite players just matter more as the elite QB's have teams contending year in and year out. The idea Belichick was sooooo much better than the 2nd best coach in the NFL as the answer to "why don't other coaches contend every year like other elite QB's do" couldn't conclusively be proven wrong, but it wasn't right.
Having Tom Brady papers over so many mistakes, can't develop 1 good offensive skill position player out of the draft in 8 years? Defense sucks one year? Don't know how to use timeouts at the end of the half even though you've been around pro football since 1976? Welcome to the NFL where all of that stuff now gets magnified.
The Patriots were also able to play hardball in every contract negotiation knowing that their team could lose anyone besides Brady and still be relatively good thus giving them an insane amount of leverage that other teams don't have. That takes a lot more balls and gumption without an elite QB creating a high floor for you every single year.