There defense is young and good, they showed that last year and I dont think they lost any key players on either side of the ball. They were all young last year and now have experience to take the next step. It isnt they have young talent and could be good in the future (that was last year). Where Missouri is at and UCLA isnt similar at all. Niether of those teams you mentioned is expected to be as good as UCLA, you just didnt pay enough attention to them last year, but it's UCLA why would anyone want to pay attention to them
And what puts the Pac-10 ahead of the Big XII to me is that USC is better than any team in the Big XII.