WSU's defense was the problem last year, not its offense...and it hasn't gotten any better this year
WSU's offense has practiced against a blitz heavy man defense, it will have a hard time transitioning against a conservative zone defense that will mix up zone coverage schemes
BYU feasted on Breske defenses when he was at Wyoming. And those defenses had more defensive players drafted and stick on NFL teams than WSU has this year.
BYU played with wide splits under a derivative of the Leach offense for 6 years. We learned a thing or two from the successes and failures of the 30+ teams who employed various schemes to defend it.
Dominating a weak defense learning a new scheme in practice is one thing. Beating a better defense against 65,000 screaming fans in the first time using the system is another entirely.