My main issue is that Mac actually regressed under Bill and the fact that Bill didn't do everything he could to help Mac succeed. A lot of it stems from the fact he seemingly doesn't seem to respect (understand?) modern offensive football. Bill is still building an offense like he has Brady and in addition is poorly evaluating offensive talent.
I know people thought I was crazy this offseason when I said that I didn't view Juju as an upgrade over Jakobi but it's blatantly obvious Bill bungled that situation. In addition he hasn't swung for the fences to get Mac a true number one receiver which has been the formula for success for so many young quarterbacks.
Bill has also completely botched the guard and tackle situation the last few years. He created holes at guard by trading Mason, letting Thuney walk (after that ridiculous use of the franchise tag), and then decreasing the offer to Karras after badly miscalculating his market. Then to add insult to injury he drafts a guard in the first round and that guard isn't even all that good. Pair the mess at guard with the disaster at tackle last season swapping Wynn (in a contract year), and Brown (who just signed for RT money) and having them both become malcontents. This year what did at tackle is just flat out negligence. Reily Reiff, who immediately was moved to guard in the summer, and Calvin "Does he even exist?" Anderson were going to protect our already close to broken quaterback?
If Bill went out and swung a trade for AJ Brown (or drafted him in the first place), Tyreek Hill, or even Calvin Ridley or Brandin Cooks (or even signed Deandre Hopkins) and Mac still failed then I would give him more benefit of the doubt. Instead he let, what would be a solid number 2, in Jakobi Meyers walk and swapped him out with a broken down Juju Smith-Schuster and doubled down on an oft-injured subpar Devante Parker and called it a day. Brady could make JAGs like these guys work but Mac and whomever the next guy is will be lightyears away from being Tom Brady so it is time to change the philosophy and Bill just isn't going to do that in his 50th year as a coach.