They should have kept the idea of an unknown man behind the mask the whole entire film with Luke Skywalker even fighting him and losing his life.
Luke’s padawan is a good Ben Solo who tries to get revenge on the masked villain for killing his master, but he ends up seriously injured.
The big reveal in Episode IX is that they cloned Luke Skywalker using his right hand, and it takes all these heroes, old and new to take him down. Rey loses a limb in the final battle.
Just as Rey is about to be killed in IX, Finn force pushes him back. Rey is shocked at his power.
Rey barely defeats evil Luke. Rey gets a new arm. Finn learns the ways of the force with Rey. They both visit Ben Solo recovering in a bacta tank. Force ghosts Luke and Leia are seen by Rey.
Ending the film with multiple scenarios for our heroes and the choices they decide to make.