A HC, above all else, needs to be a great leader of men who is an expert in the following:
1. Hiring a great staff that develops players and plays to the strengths of the talent he can acquire;
2. Keeping his team playing at a peak emotional level from week to week and pushing all the right buttons to achieve that goal (see dudes like Saban and Lance Leipold who get this done week in and week out and never allow complacency to set in).
The HC doesn't need too be some great football scientist capable of out scheming everyone. That's what he hires his assistants to do. He needs to be a great leader and button pusher who demands constant excellence and attention to detail.