LSU alumnus and fan here. Aranda is a very good coach and no nonsense kind of guy. He's been one of the best DCs in the country the last 5 years even though statistically, his best year as DC was in 2016, his first year at LSU. The defense you saw in the first half of this season was pretty uncharacteristic for that program. The defense that showed up in the second half of the season (when everyone was finally healthy) was more like one of his defenses of year's past. Talent, of course, has a lot to do with that.
Personally, losing Joe Brady hurts a bit since he brought a whole new perspective to Emsminger for the offense however, they should be ok on that side of the ball even with all the attrition (Burrow being the most obvious one).
On the other hand, losing Aranda might be much harder for LSU to recover from. Unless Orgeron is able to hire Venebles from Clemson (doubtful) or Grantham from UF or someone of that caliber, it's going to feel like a big step backwards to me.
