On this point, it would be an interesting study. I really don't know but have some theories.
First, the best coaches tend to go from OC or DC to head coach -regardless of race. Some take G5 jobs, succeed, and then get a P5 job, but generally most of the "top" coaches get their first head coaching gig at a P5 from another P5 coordinator position, so the better ones skip the G5 route. Like we may be experiencing you see coaches go straight from position coach to G5 head coach. They miss out on some of those experiences jumping straight into the CEO role (as HC) that are needed to truly understand how to oversee chief operating officer roles (i.e OC and DC). This is magnified for black coaches because they get fewer opportunities for those OC and DC positions than do white coaches. Just the unfortunate reality.
Second, I have to imagine there's a lot of psychology at play. An immense amount of pressure put on themselves knowing they are one of the handful of black coaches at the FBS level. And what that's like having to constantly feel like you have to prove yourself on the field, with boosters, with fans, with administration, etc. I think you put these two factors together and it's creates an environment that doesn't set these individuals for success.
And until that changes I don't think this is the route we should go, because the chances of success here without those experiences is pretty remote. This is why I like Willie over the others. He's already proven ability to lead and run a program.