I never think that a good coordinator automatically makes one a good coach. The game changes, and what worked one season, may not work the next.
A good Head Coach is the CEO, who manages the team, builds the team culture and identity. Coordinators come and go, but the team identity stays. Saban has to deal with new coordinators every year, but he still is successful because as the head coach he only deals with the big things, and not the minutiae, that’s what the assistants are for.
In all fairness, at least Saban has a professional offensive line to work with.