re: How much can the o-line really improve?

Honestly, quite a bit. the top indicator for offensive line performance is returning line starts. This season, the top three teams in the SEC in Football Outsiders' Adjusted Line Yards and Sack Rate were 2nd, 5th, and 1st in returning starts, respectively. The bottom three teams in those stats were 7th, 13th (LSU), and 12th in returning line starts.

There's some exceptions (Vandy returned a ton of linemen and well, they still were below league average and Georgia outperformed its lack of experience), but those can usually be attributed to the next factor: raw talent, which LSU has. LSU's line should massively improve by virtue of its experience. They returned just 35 career starts last season, and I think that was calculated before Ingram got suspended. So it was actually worse. This line was starting almost literally at ground zero. By contrast, Bama had 103 career returning starts. It showed.