BB is not just the coach of the Patriots, he's the decision-maker at the top of the entire football operation. I doubt he would even want to return to a coach-only role, at least on this team. But in any event, the current team on the field is all his responsibility. The players and coaches are the ones he chose, or his people did.
We are on year 5 of the Pats not being a SB-caliber team, starting with Brady's final year, followed by the Cam Newton/Covid year and the three-year Mac experiment.
I think the best case that could be made for BB at this point is that until now, his focus has been on extending the dynasty rather than on rebuilding. Because of that, and a (surprisingly in retrospect) pretty good rookie year from Mac, what might have been a shorter, faster rebuilding process has become a slow and painful one where the team is still going to hit rock bottom but it has taken much longer to get there. What is happening to the Pats now would have happened to anyone, and if BB erred at all here, it is in thinking he could do a rebuild on the fly.
If you don't buy that case, I think the only alternative is that BB's best days are way behind him, managing an entire football operation is beyond him even though he can still do some good coaching things especially on defense, and instead of being the best football operation in the league as we are used to, they are actually one of the worst. Why?
1. Talent acquisition and retention on this team is bad. This is a team whose only playable QB is bad. Its OL is bad. Its WRs are bad, save for a 6th round pick who is looking like a real find to be our next Welker/Amendola/Edelman type. They let a WR, Jakobi Meyers, who had good chemistry with Mac leave in order to pay basically the same money to a guy whose knee is a mess and who doesn't fit here. They haven't effectively plugged offensive holes via the draft or free agency.
2. Coaching staff turnover has been a major factor. They had no McDaniels succession plan in place despite knowing the guy would get HC offers and the best they could do at the last minute after he left (taking half the offensive staff with him) was put the offense in the hands of a defensive coordinator and a special teams coach. Under these two, the Pats attempted a major revamp of the offense for the first time in BB's tenure. It went, predictably, badly.
3. There is a real breakdown in the team's traditionally strong execution.
4. They don't appear to understand how rotten this team was at its core. They finally did the coaching staff revamp that should have happened a year ago, didn't make any major moves in free agency, and thought that a little lipstick on this pig was all that was needed to field a team that could compete with Miami and Buffalo.
Maybe #4 is wrong. Maybe BB went into this year knowing full well that the team was a mess and that the season was going to be awful, but that they finally decided that the crash and burn strategy was the only path forward. They just didn't signal that. If that's true, it's a point in BB's favor.
And maybe this kind of process was inevitable after years of good records leading to poor draft position, etc, and maybe BB drew things out by managing to be competitive with smoke-and-mirrors as the team deteriorated.
But I think that's the choice - either getting to where we are now as a franchise was inevitable or BB is over the hill and no longer capable of running the operation. If the latter is true, he's not the guy you want to entrust with a rebuild.
But there's no excuse like "Well, he's stuck with a poor QB else the team would be much better," because the QB is the guy he brought in, gave the job to, and didn't bring in a playable person to back up.