Here’s what I have learned in the divisional games… The HC only matters a little bit.

I don't mean to pick apart your post but its the only way I can answer your question, or at least address em to some marginal degree.
  • i don't know if he can build from scratch. not saying he can't, but his successes that put him on the radar to promotion both involve taking a "good" situation and tweaking it to "great". he's proven he can make improvements, maybe even ELITE improvements; but can he build from nothing, or elevate "average" to great. his one chance to demonstrate this was the Panthers, but he was fired before we could learn whether he is capable. the question remains unanswered.

This wasn't completely answered with the Panthers, but in his first year Teddy Bridgewater and Mike Davis both had career years, which indicate that its more likely then not.
similarly, I don't know if he can sustain what he's built. he's parlayed his success into promotions elsewhere, so he hasn't been able to demonstrate an ability to duplicate his success in a repeatable fashion over more than 1 season. again, not saying he can't, but haven't seen that he can either. this question remains unanswered.

Joe brady took over the Bills offense starting December in 2023 and the Bills won 4 straight because of their offense. This gave coaches 4 games worth of game film over the offseason to look back on. But Brady kept that offense not just performing well, but consistantly good.

Again, not a large sample size to say with confidence, but it lends to the leaning of a bit more likely then not and hints at the capability.

Brady certainly has a low floor. But he and Ben Johnson are the only two coaching candidates that I can see with a very high ceiling. All the other coaching candidates from McCarthy, Kafka, Glenn.... All low to average floors, but also all low to average ceilings. I just have zero interest in shooting for average.