Guys, this probably wasn't as one-sided as all that. PK is a unique guy. We've talked about how he was a savant for designing defenses, but couldn't talk to a recruit. There's every reason to believe that the relationship just got stale after awhile, and that neither PK nor Sark was happy with the situation.
The idea of Muschamp is near and dear to Longhorn fans. Pictures of him bleeding from a head wound on the sideline, punching diagram whiteboards in front of players, and of course the yelling "Boom, M'f'er!" after a big hit still play to the fans. In the 2000's, his defensive game got lots of HC offers. Texas kept him around with pay raises and the idea that Brown was planning a graceful retirement. When that retirement was "delayed", he reportedly regretfully moved on.
His record as HC is positive but not overwhelming. Spent the last couple of seasons with UGA as an analyst. Reportedly, he really loves Austin. Good chance he and Sark have complementary energies. I believe he'll have a better eye towards how to defend SEC style offenses (odd how these align more than would be necessary) than PK.