Bobs biggest mistake was not acting as the peacemaker between his two superstars. I do believe the relationship needed mending, and it needed attention much earlier than most think, like 2016 earlier. I do not believe it was irrevocably broken, but thats my opinion only. I do not think he did enough to help mend fences. By the time Brady told Bob his decision to leave, it was already too late.
The relationship between RKK and BB soured immediately when Tom did what Tom does, win. I believe, with absolutely nothing to back it up, RKK became covetous of Bradys 7th. That put BB on notice, placed a big ass target on his back, and he could not or would not, depending on your point of view, adapt quickly enough to move the franchise forward. Tough thing to do, replace the greatest player to put on the pads, no?
Ah well... its the past. I choose to remember the good times. No reason to wallow in the bad.