Yes the head man has his philosophies and is in control of the team. But if your position coaches do a lousy job of coaching up your players you will not be very good, period.
Most of these kids do not get good coaching in high school. They don't magically learn the college level technique overnight. They may be talented but they do not know the nuances of their positions.
Why have Urban Meyer and Nick Saban dominated college football? First of all they are great recruiters. But possibly even more important they hire all star coaching staffs that get everything they can out of their players.. How many of their assistants are now head coaches/coordinators? Coach in the NFL?