The Birds have had three seasons in a row under the present head coach, three seasons during which they had great first parts of the season followed by collapse. This head coach's record as a college coach had the same problem.
My theory is the coach is good at putting together a system and plays which work great until the opposing teams figure them out. Kind of like how a new baseball pitcher can be a marvel until everybody scouts him.
I'm just guessing, since I haven't watched a football game in years.
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.