Tebow is the perfect QB for Meyer's system. If you had a QB creating machine and could put in all the attributes you desire for a QB, then Tebow is exactly what would come out if Meyer was the one creating the QB.
That said, Tebow still needs coaching to be good. You can't just run him out there and have success.
I think that Meyer promoting his OL coach to the OC post definitely suggests that Meyer is the main man in charge of the offense, and Mullen's job was likely to understand what Meyer wanted and make it happen. That said, that doesn't really have much to do with whether or not Mullen can or will be a solid head coach. I'd say that at least 75% of being a good head coach has to do with your ability to hire good assistants and manage the program. If he's done well at hiring assistants to balance his weaknesses, and he's good at delegating, he'll do a good job.
I go back again to Tuberville. I always thought his ability to hire assistants was a lot of the reason for his success, and I think his ability to pick up the slack for the weak spots on his staff was the reason he lasted so long. In the end, it was a poor assistant hire, that seemed forced on him, that had a lot to do with his demise.