A good to great coach in today's NFL does not have to be a brilliant X's & O's kind of guy, but he does need to be more than competent. More importantly, I think he needs to be a great leader. The signs are there for Fox. Of course, he needs to win a SB or two to get into the great category, but I think he will.
It is obvious that the players like to play for him, but he also has a very good well-respected staff that is very loyal to him. The only defections are promotions like Allen & McCoy. This is a complement to the HC, and says a lot about his ability to surround himself with very good people, by putting his own ego aside. Do not underestimate this attribute.
McD's ego, amongst other reasons, got the best of him. For example, when he had a good coach, like Nolan who himself was a HC and probably has an ego also, McD tries to micromanage and he eventually chases off a talented coach like Nolan. Then we get stuck with Wink because he will be subservient to the boss.
Anyway, this season will be a big test for Fox, and Manning for that matter. If the team goes 1 and out in the post season, I am not sure he gets fired, but surely Elway will put some heat on him. OTOH, if he gets the Broncos to the SB, then he did his job and he can contemplate his retirement exit into the sunset.