I think a little of the defensive problems are with PJ's offensive scheme. I think it really does hurt the guys (to what extent I don't know) to never go up against starters that have a pro style, or pro style spread (like Alabama, Florida, UGA, FSU, Clemson, etc. in practice/camp. If we were a pro style offense they could play against the starters in camp and get some reps in preparation for teams that run similar offenses. I think similar issues occur with Gus Malzon's offense. Auburn hasn't had a good defense since he's been there.
The other problem is that Ted roof isn't a great coordinator. We shouldn't have canned Womack so quickly. I know Ted is a good recruiter and a tech man, but he doesn't have a history of good defenses. His best defense was at Penn state, but I attribute that to style of play, and more importantly Bill O'Brian.
But, the main issue is probably horses on the DL. We just don't have them, or the guys we have aren't being coached very well. Great defenses get pressure with 4 and we simply cannot do it.