Maybe i wasn't clear, sorry. They'd have to fix Ravus and Luna's models in the movie. That is key and first priority. They should honestly do it anyway, regardless if they added scene or not.
What I was trying to get at was sprinkling important events/scenes from the movie to the game as you find out about them. Noctis doesn't know Luna has the ring until after Chapter 9. Imagine him receiving the ring, then in comes a 5 minute CG sequence showing you how she even got the ring in the first place.
Also, the first 4 minutes of Kingsglaive are almost vital to understanding the main conflict if you've never kept up with the game's lore. Its silly to me how much of it was left out of the main game. Kingsgaive's bearing on the main story is extremely important, even if it is through the eyes of a different character.
Im also not saying add in the entire 2 hours of cutscenes into the game, but rather, make use of the decent CG (maybe 30-45 minutes of it sprinkled throughout the 25 hour main story) just to tell the story thats needed.
Luna's, Iedolas's and Ravus's characterization, The Treaty Signing, Regis's death, Drautos's betrayal, and Nyx's sacrifice are all really important parts of the main games story, even if the last 2 do not have a major effect on the story, they are the reason Luna got the ring in the first place.
