I have found that guys that are "guru" on one side of the ball generally fail as HC. I am not sure exactly why but I assume it is because they can't wrap their mind around the whole package.
Marvin Lewis may be the exception but he has had 9 years of on the job training.
Pretty much anyone from the Andy Reid tree
Lots of great coaches were generally unheralded as coordinators
See the Harbaugh's, Tomlin, Dungy, Cowher
That is why I definitely want to avoid the guru coordinator if we can Philbin.