I am more concerned about AB perimeter blocking than defense:
Snoddy's strength is running. Searcy's strength is receiving and running. Lynch I'm not sure on. Willis is probably the best all around guy when blocking is considered. So it makes a lot of sense to beef up AB with MLD and Jordan, IMO. Particularly when WR blocking is considered. Summers is pretty good in that department but I'm not sure about June. Stewart has showed out in the passing game so far but PJ has said "he needs to get stronger" which I'm wondering means he isn't physical enough to block well yet. Messick I am hoping shows up big in the blocking department.
My observation of our D last year was that the fundamentals got much better as the year went on. Specifically we hit harder, tackled better, and took better angles. I thought pass rush and getting off blocks continued to be an issue.
The improvement was on display vs UGA when we stonewalled their run game in the second half. Forced to live through a lower percentage air attack (incompletes, holdings, sacks, ints), UGA had trouble sustaining drives, including their OT drive where DJ comes up with the pick. Meanwhile we scored with mostly FB dives in OT.
Orange Bowl was a carbon copy. Did we give up a bajillion yds through the air? Yeah. Did we stop their runs? Yeah. Did a lot of their drives end in incompletions, sacks, ints, etc? Yeah.
I'm not saying our defense was good last year. Only that it got better, and that improvement was fundamental and mostly in stopping the run. Question is will improvement continue? Roof's record suggests it will for one. He has turned around horrible defenses at GT(1st stint), Duke, and Minnesota. Roof's D's historically hemorrhage passing yds between the 20's in favor of stopping the run while looking for the drive-stopping incompl/int/sack/fumble/penalty. If no stop comes he will seek to stop you in the red zone where it's harder for you to score since you can't run it well and the field is compressed for passsing.
Problem was last year our pass rush stunk and early in the year our fundamentals were sketchy still vs. the run.
Upfront this year we should win more 1-on-1 battles in the pass rush. Hunt Days and Gotsis look good at DT, K-free is an emerging star at DE, and Simmons and Whitehead should help K-free provide a rush on obvious passing downs. Gamble is a capable DT and can be inserted at SDE to help shut down the run. Kallon provides some depth. At DE we have some other guys in Rook, Stargell, and Merriweather who may develop and certainly won't be worse than last year. There are more and better horses to work with.
At LB PJ Davis and Macordes have played a bunch. Macordes was strong when healthy and can rush the passer. Terrell Lewis looks like the real deal as well, and Hankins looked good end of last season.
Secondary I'm not that concerned. All four positions are occupied by vets, and behind them we have some good players.
So I see D improving at least one very noticeable order of magnitude, and I fret about perimeter blocking.