He may be a good coordinator, X and O's guy, but definitely not a leader of men. All one has to do is watch the in season Hard Knocks to see how awkward and out of place he is as a 'leader' - would be comical if it wasn't so cringe. There's a reason why his word-salad-spewing, nerd/'quirky' persona was so against the typical NFL HC grain - because it doesn't work.
I agree with your last sentiment - no one really knows how hard being a HC is, but sometimes it's easy to see when someone doesn't have what it takes