Sweat staying back for another year was a huge win for the defense. Collins hasn't lived up to the hype, but I'm glad to have him in the rotation. To write off either is foolish, particularly when they'll have as much or more help at NT and EDGE to support them than we've seen in previous years.
The defensive line will be anchored by Sorrell and Murphy anyway, and the rest just need to be competent to match last year. Throw in an improved pass rush with second year Burke and Finkley and the raw talent of Colton Vasek and Anthony Hill, and hopefully all those QB pressures start to result in more sacks. This seems to be the plan, and I don't see how it won't result in similar results on run defense with a chance to improve our pass defense up front. ILB will be the same or better with Ford at Mike and your-guess-is-as-good-as-mine at Will (same as it ever was).
You can nitpick individual players, but I think there's plenty of room for optimism for the defense as a whole. You either believe that PK, Davis, and Choate can coach this combo of talent into a serviceable front 6 or 7 or you don't. I choose to believe they can. Combine that with what appears to be the most talented secondary we've had in recent memory, and I see a defense that has a floor that we can win the Big12 with.