Unfortunately, the Pac-12 moved away from great defensive coaches and the quality of football has suffered over the last five seasons. Losing Carroll and Harbaugh seriously brought down the overall quality of the coaching, and so did losing Chip Kelly for other reasons, although I think his style of football put a lot of stress on his defenses and made it hard for them to win a national championship.
Stanford has been the only team to play consistent defense during that time, so it is no surprise that they have won the conference two out of the last three years and appear primed for a third conference title. However, Stanford's academic standards become somewhat limiting for them . . . it forces them to scour the country for a certain kind of student-athlete and creates a ceiling on how much they can achieve on the national level.
USC has as much talent as anyone, thanks to the brand that Pete Carroll revitalized, but the sanctions coupled with bad defensive coaching have limited what they have accomplished since Carroll left. Their AD seems committed to continuing to neglect their defense in favor of another Kiffin/Sarkisian-like HC/play caller.
In that vein, Mike Leach is another coach who could not care any less about supporting his defense. Like a hammer hitting a nail, he will be decimated by Stanford.
It has been good to see Washington finally showing a commitment to defense. The defense has kept them in most games this season and has given us hope for the future.