Was Grump Luke JJs idea? It seems to have come from Johnson.
Well, JJ kind of came up with the original idea. When talking about why Luke went away, Han says this line:
“He was training a new generation of Jedi. One boy, an apprentice, turned against him and destroyed it all. Luke felt responsible. He just walked away from everything.”
So the seeds were already planted in TFA, although Rian took that idea way beyond what JJ intended.