I think it all starts with poor line play

Alabama got one o-lineman from LA. Calm down. But you are right, the root of the defense's problems start at the line. This is as bad a group as LSU has had in probably 15+ years. They generate absolutely no pressure, ever, and they struggle to stop the run. It filters its way on back. The worrisome part is that you brought in several D-lineman in your last recruiting class and they can't see the field even with the starters being below avg. Certianly the young guys could turn out to be great, but you still have to have some concerns.

As long as Miles has been here, LSU's pass protection has been good, but not great. However, a lot may do with the fact that the offense has been very predictable. Opposing SEC DCs will tell you that LSU's offense is easy to prepare for. When you only tend to throw in predictable passing downs, it makes it a bit easier for DC's to bring more people than you can block.

At their core, Miles' LSU teams have been a very basic group scheme wise, but with outstanding talent. But you see what happens once that talent advantage starts to shrink a bit