I mostly agree with you but theres a few variables. Yes, Nuss will improve quite a lot, but let's not pretend LSU's offensive play calling was good last year. I may be exaggerating slightly, but you could debate the play calling was bad.
If the play calling turns out similar to last season, its possible Nuss doesn't end up being a top 5 pick. Then again, it may not matter. Look at Dart. His struggles last season weren't because of him, but mostly because of how bad the Ole Miss offensive play calling was. He started the offseason as a estimated 3rd round pick and has now climbed into top 10 pick as people have watched game film, watched him play, and recognize the play calling was doing him a disservice.