Well The ROS was focused on Rey like Return of the Jedi was focused on Luke. It’s not the prequel trilogy Kylo is not the main character. Vader was not the central character of the OT either.

Lukes story purpose is given to Rey though, restoring the Jedi order. Passing on what he had learned.

We still don’t know why the New Republic failed or was incompetent and had no army to fight the first order. Or what happened to the Empire. Or is the New Republic going to be restored post ROS since it clearly failed. And Luke, Han and Leia were failures.

I suppose some of these things are described by Disney in novels and comics. Goody more homework. They made Star Wars like MCU. You have to watch a bunch of shows to explain their bad movies. If they even fill in any blanks at all.