Tui could've stayed at Washington and learned from one of the best, but instead chose to stay with Sark and his undisciplined bullshit excuses. That says a lot about Tui's decision making and how he perceives short term/long term value. So in short, fuck that guy. Money now in exchange for learning how to be a good coach.
That's assuming Peterman even wanted him. I know the media reported he had an offer, but who knows about the validity of that. He's not one of Petersen's guys. He went with the staff he was familiar with for more money.
The whole coaching under one of the best is mostly a bullshit myth. Urban Meyer coached under Bob Davie at Notre Dame before getting the Bowling Green head coaching job. Sark and Kiffin coached under Carroll. Which guy learned from the better coach? I could name a whole bunch of other assistants who coached under great head coaches who went on to suck.