BYU would have had a defense good enough to support success with KW, there really isn't any question that KW is one of the best defensive coaches in the country.
If he has a good OC, he would be good just about any situation.

We probably also wouldn't be fielding the army of Helaman, but KW knew why Crowton was fired when he was contemplating the BYU offer, and football wins wasn't the main reason. KW made a fiscal decision ultimately, but he was very close to becoming our HC.