Well lets look at last year's defense fairly. Was it really ever that good?
Game 1 against Georgia Tech we struggled, maybe the best ACC offense we faced?
Indiana was terrible, Boston College wasn't a good offense, NC State was laughably bad on offense, Pitt wasn't that good and scored on us, Duke was playing an injured QB, VT wasn't amazing, UVA wasn't special and they were driving on us at times.
Miami was playing Van Dyke after he was benched, even he looked decent against us. Kentucky struggled all year and could move it on us. FSU didn't have a QB. USC played backups and ate us up.
Notre Dame was probably the only good offense we stopped last year in my opinion. But even they didn't have a great year. We didn't really play any of the top tier QBs in our own league last year. I think we had an advantage not having to play many good QBs last year and the defense looked a lot better. We also lost 2 NFL talents in the secondary.
This year we're playing way better talent.
Georgia Tech is much improved in 1 year. Notre Dame & Leonard on the road. SMU is a high powered offense. Miami and the likely Heisman favorite. 2 weeks we'll play a talented Clemson team too. So we're seeing a lot more talent this year than we did a year ago. The signs were there late in the year from the UVA game until the bowl game, I think the film got out and OCs have figured out how to attack us.
I kind of got worried during the UVA game last year, but thought it's one week. But then Miami and Van Dyke carved us up, just made some big mistakes. THen Kentucky made big plays. Then USC. We're really more relying on turnovers for our big plays, but we can't really stop a team consistently.