I don't think what a coach's experience as a position coach, coordinator, or what he was in NCAA has any bearing on how good a HC he'd make. I do know that there are a crapload of coordinators who became HCs and sucked at the job. Most of them in fact.
I think the problem is that other than the intangibles, the skill set of being a successful position coach don't provide much of an indicator of whether a position coach will make a good coordinator, and there certainly are no duties of a coordinator that will predict success as a HC or the failure rate wouldn't be so high.