I think it's evident that Bill was right about Mac, but he sabotaged himself by installing Patricia as the OC. It was too easy to point at Patricia as the problem even if Bill was right that Mac was regressing, teams were figuring him out and he was not elevating his own game, and he had some slight attitude issues. Additionally, Bill's poor drafting and hit-or-miss free agency decisions made it such that the problems on the team were myriad and hard to point to one single thing. If the team was fairly well-built, with a fairly respectable OC, and the QB play was bad, it would have been an easy sell. Bringing in Bill O'Brien at least somewhat solved the second issue, which to an extent proved that the QB was not good, but the team overall also got even worse, so it was really too late anyway.
I think the critical failure here was Bill's ego hiring his friends in 2022. If he could have put that aside and allowed himself to bring in and work with someone he didn't know well as his OC (and I can't imagine he would have had a hard time finding some good options, he's the GOAT), even despite the roster struggles he probably would have more successfully sold the idea that Mac isn't actually good and they need to move on while also not losing his own job. I guess maybe that's what happened in some alternate universe.