I think even lower division HC experience is very valuable. Obviously the management and PR duties, etc., are not comparable between DII and FBS, but the game is the same game and there is a very different perspective one gains from being in charge of all planning, preparation and game management decisions rather than just being an assistant.
Carlen was hired without any HC experience at all (and he was very young) and though he obviously did well it was a different time. Even Cignetti had been a HS head coach earlier in his career.
Holgorsen might again prove to be a very good OC, but I think he needs a wiser, calmer boss who grasps the whole game to rein in him and slow him down and prevent him from making mistakes his lack of perspective causes. Assessing field position, down and distance, time remaining, use of timeouts, and flow of the game are not among his strengths. He has improved slightly in some respects over 5 years, but he does not seem fully capable of tailoring decisions to the situation because of his obvious infatuation with playing fast and his stubbornness that prevents him adapting well to his personnel.