This was really interesting to find out, good post. Liked.
BK was crazy good at getting consistently solid production from the run game with position transfers, and lower rated players, and developing lower rated/underappreciated prospects into NFL draft picks. I think BKs offensive lines/system helped increase the illusion of the quality of RBs though, based on their lack of draft stock, but I digress.
Part of being a head coach in college is creating a program and culture that attracts super talented athletes, and that is the part where\e Kelly failed. You gotta have both the traditional head coach skills but also a lot of charisma and personality that talented kids with a choice to go anywhere want to be around for the next 3-5 years.
Can you imagine if BK was also an elite recruiter and had some combination of Reggie Bush + Mike Williams at the offensive skill positions like Pete Carroll had at USC?
That kind of star power was elusive during the entire BK era though which is ultimately what limited the program's upside under him.