I have to respectfully disagree w/ part of ur post;
Yes, the greater majority of good to great coaches/ coordinators are guys who were not stars at their sport, but the vast, overwhelming majority of these coaches played the sport at some level, whether it was D-I, FCS, D-IAA, or D-II. U brought up Glenn Schumann, but what u didn’t bring up what sets him apart from Diaz is that he’s the son of Eric Schumann, who played DB at Bama & have been a DC or position coach since 1986. There’s a lot of young coaches, The Lombardis come to mind, where they grew up in a football household, but may not have played the game at that level. Diaz, on the hand, grew up in a household of politics.
So there’s a stark difference to that exception. No, Glenn may not have played the game at the collegiate level, but he was born into that arena, which is y he immediately applied to be an assistant to Saban as soon as he enrolled at Bama, and being a legacy, he was ahead of the pecking order.
Even Mike McDaniels played college ball at Yale for a bit. Again, VERY rare do u see coaches or coordinators not play ball at some level, collegiately, & if u do, u bets believe they come from a football family.