I also think you underestimate how Bama feeds Saban's ego.
...and he's turned down NFL offers for the last few years.
Just sayin....
At some point...Coach Cut was gonna test his skills as a HC, IMO
In some systems...the revolution speed of the revolving door varies.
When Gruden shows up in Knoxville...I bet out assistant coaching door slows waaaaay down relative to the last 4 years.
At least for a few years.
Maybe it was loyalty, maybe it was the caliber of assistants Fulmer had, maybe they just weren't ambitious, I dunno...but aside from Garner & Cut, I don't recall a lot of attrition.
I'm just saying, it's not a "constant" with every staff, however, with Gruden's it most certainly will be.
Bama is almost a model for the type of situation that you are describing. They are the most successful college program since Saban took the job and they do have staff turnover. The difference is that, just like their football roster, quality candidates are ready to take the job.
Winning cures all ills...