In a nutshell, even if you think he is a great football mind (debatable), his approach to coaching is better suited to the NFL than college. In college football you are a politician, in the NFL you are a CEO. He wanted to be a CEO, but all of his VP's walked in year 2 and he hired Sunseri to replace them. Sunseri may be a great coach, but you don't change to a 3-4 when your job in on the line. First year of a 3-4 is almost always bad, even bama went 6-6 year one...
Also I hear stories about how he never called any of the HS coaches around Nashville, leaving that to his assistants. That works fine for a CEO but these HS coaches felt like they sent an email to their congressman and got a generic "thank you for your vote! form letter in return.