I still contend that the biggest leadership mistake that he made was changing too much from a program that was doing well by MSU standards. If he had simply promoted Spurrier to OC, and did his best to run the program in year 1, the way he saw Leach model it, he could both incrementally learn how to steer the ship and make small changes along the way that suited his style and program success. Two totally different situations that Croom v Arnett walked into.
When Croom came in, the program needed major change, he just wasn't capable of successfully leading through that change. When Arnett came in, it was allegedly for continuity and because it seemed like the best response to a crappy situation. He needed only maintain/learn this year, but he chose to change everything on offense and create a rebuild year out of thin air.