It's kind of worth looking at the 2015 season. Coker, against the #2, #1, and #3 team had an average rating of 175. That includes his performance in almost mirror image to the LSU game, 45-40 win over Watson and Clemsons.
Tua against the 3, 3, 4, 4, 2, 2 team (that includes both his Georgia games) had an average rating of 153.
The results in the biggest game aren't any better than Alabama's offense circa 2015. This "modern" pass heavy offense might not really be better. On the other hand, the 2015 defense still gave up 43 to Ole Miss and 40 to Clemson though. The 43-37 loss to Ole Miss played out a lot like this LSU game (Coker did have two turnovers that game, but he came in as a backup and played from behind).
The moral of the story? You get into shootouts and all defenses look bad. You turn the ball over in a tough game and you might lose. You play well in big games and you can win championships, even if your defense gives up 40 points. I don't see a fundamental problem on defense, I see a defense being put in bad situations.