Their defense was #1 in scoring defense and turnovers in the Pac 12, and returns almost everyone. I'm not sure where you got this take from. UNLV had 2 nice long drives to start the game, and then basically nothing. They had 155 total yards I believe, 90% of which were in their first 2 drives? They were stonewalled the entire 2nd half.
Maybe BYU will run all over them. We'll have to see. The power run with a mobile QB is very dangerous... But if you run and score on ASU like you seem to expect to, it's because BYU is very, very good. Not because ASU is soft. This is more than likely the best defense on your schedule.