The system doesn't matter, you can win with any system given you fill the roster with the right players. It's all about getting recruits, way more so than X's and O's or gameday coaching. IMO, 95% of a coach's success comes from work done prior to stepping on the floor...recruiting, practice, scouting, film, gameplans, etc. Sure, there are some adjustments made at halftime, but a vast majority is already in place before the ball is tipped. It's not like these guys are drawing stuff up on the fly...the players have already been through the situation in practice.
I'm sure Terry Evans is a good coach, but hiring him is basically taking a leap of faith and saying "well I hope he can recruit at the D-I level", which isn't very assuring compared to other possibilities. You are hiring Terry Evans on a hunch that he will be good and the fact he loves OU. Sorry, but that doesn't cut it.