This has been discussed before, but with the recent news regarding Belicheck being possibly fired (which blows my mind) and Josh McDaniels getting fired (again), it bears repeating.
Bill Belicheck - he's 87-97 after Tom Brady left.
Charlie Weis - he went 35-27 as the head coach of Notre Dame and 6-22 at Kansas in college after leaving NE. His one year as Florida's offensive coordinator in 2010 his offense was 102nd.
Josh McDaniels - He went 11-17 as head coach of the Broncos, and 20-33 as head coach of the Raiders after he left NE.
Bill O'Brien - He went 15-9 as Penn State's head coach, then 52-48 as Houston Texans' head coach after leaving NE. He did make it the college national championship game with Alabama in 2021 but lost to Georgia.
Romeo Crennel - yes, he's on the defensive side. However, he went 24-40 as Cleveland's head coach after leaving New England, then went 4-15 as Kansas City's head coach and 4-8 as Houston Texans' head coach.
Eric Mangini - yes, another defensive guy. However, he went 23-25 as the Jets' head coach after leaving New England and then 10-22 as the Brown's head coach.
Bill Walsh was 17-23-1 without Joe Montana.
Clearly Bill Walsh was a fraud who was exposed without Montana.