blowing people out and putting up huge numbers quickly will also get the first teamers out of the game much quicker than normal, as well. and the 2nd/3rd stringers are usually the ones conceding the garbage scores that make it look worse than it really is.
bama's adjusted d rankings are #2 in FEI, #8 in sp+ and #9 in espn's def efficiency. according to reddit bama site, anyway. i'm guessing lsu's is similar.
I don't think we have many first-teamers left in the front 7 since Texas

I can't find FEI right now, so I don't know where you're getting that, but LSU is way down at 35 in SP+ defensively. Obviously those numbers don't mean as much as they will a month from now, but for whatever they're worth at the moment, LSU is not up in the category with Bama/UGA/UF/AU/Big Ten teams listed, on a per play basis. iirc, that's what SP+ is, whereas FEI is per drive basis, so I wonder if we fare any better there or not.
Just quickly looking at Alabama and OSU for comparison's sake:
Our % 3rd down conversion allowed and drives ending in punt/turnover on downs is right there with Alabama and OSU. LSU is well below those two teams in drives ending in INT/Fumble recover (also forced fumbles). LSU is also 7% higher (bad) than Alabama and 13% higher than OSU in drives ending in something other than turnover, turnover on downs, or punt (not my research, I'm assuming the guy means "drives ending in points" ?).
We know the tackling needs to get better, but what jumps out at me from that list is LSU is not capitalizing on it's excellent number of passes defended, turning only 2 out of 27 into INTs. You would almost expect some reversion to the mean there, but just eyeballing it the DBs have butterfingered a few notable should-be INTs. Contrast that to Alabama who has 6 INTs out of 19 passes defended (a rate that may also revert down to norms). LSU is 10th in the country at passes defended but 85th in INT/game. Also middle of the pack forcing only 3 fumbles. Basically LSU needs to tackle better, do better in all phases of turnover opportunities, and get healthy if possible.
It could amount to the same thing, but it "feels" different than say, 2013 or 2017 when LSU's defense disappointed, mainly because the horses just weren't there. It seems like there's hope for a top unit here, although I doubt the pass rush will ever be elite with this group.