LSU plays in a conference full of primitive offenses that make an opposing D look good. Things look a lot different when they run into competent, modern offenses.
Georgia was averaging 18.5 PPG before the bowl. Texas put 28 on them even trying to run the clock out for most of the 2nd half.
Bama gave up 14.8 PPG. OU scored 34 and Clemson 44 against them.
Mizzou's D averaged 24.4 PPG. Okie Lite barely qualified for a bowl game. The Cowboys had a 3-6 record in the Big XII and scored 38 points.
Vandy surrendered 25.1 PPG. Like OSU, Baylor barely qualified and had a losing record in the Big XII. The Bears put up 45 in the bowl.
Objectively, Big XII offenses were much better than those of the SEC in the 4 inter-conference bowl games. Texas outscored UGa's average by 9.5 points. OU went 19.2 points over Alabama's average. OSU was a lower tier Big XII team and exceeded Missouri's average by 13.6 points. Baylor another lower tier team from the Big XII beat Vandy's average defensive effort by 19.9 points.
On the flip side of the coin, Texas averaged 31.1 points scored with 28 vs Georgia. IOW, the 2nd rated defense in the SEC was 3 points tougher than the average defense in the Big XII. Alabama did manage to keep OU 15 points under their average but that average was so high that Bama looked merely above average, not utterly dominant as they did against the SEC's crap offenses. OSU was right on their average so Mizzou performed like an average Big XII defense. Finally Baylor was scoring 28.3 PPG coming into the bowl. Vandy's D was 17 points worse than the average D in the Big XII.
When you look at actual outcomes, it's clear that any claim of tough defense in the SEC is the result of how bad the offenses are in that league. The same defenses look MUCH worse when pitted against modern, well-coached offenses - even those with significantly less talent. Put SEC teams through a Big XII schedule and I guarantee you that most of them would give up north of 30 PPG. The proof is in the pudding even if it is a bitter pill for the SEC homers to swallow.