One of the hardest things in sports is how to identify a head coach (football, basketball, hockey) or manager (baseball, soccer). In football, most times a coordinator is raised up to HC, assuming success as a coordinator transfers to success as HC. That seems to work maybe, at best, around a third of a time. But the only way you find out is to give a guy a shot.
McDaniel seems to be a classic example of a guy that was a good coordinator but tops out there. Peter principal hits again.