This is a *spectacular* misreading of what happens. Luke, in his final moments, act as a true Jedi unlike anything we’ve ever seen in the movies. He redeems the concept of what it *means* to be a Jedi as Yoda explained it to him. Teachings Yoda *himself* forgot in the Clone Wars.
Luke used the Force, a MASSIVE amount of power as Kylo implies earlier in the movie, to use the Force for defense (never for attack) to save the spark of hope that could save the galaxy. His story spreads, as we see at the end of the movie, becoming even more of a legend than he had ever been before. I’m the end he’s gone from a man to Hercules, a hero of myth, that can never be corrupted.
Honestly, I can’t see how anyone can be disappointed it Luke Skywalker’s arc. He goes from a rote Joseph Campbell archetype to one of the greatest fictional characters of all time.
That was the failure. That was his greatest failure, and what drives him to isolation. Because, as established in literally every movie Luke is in, he runs from his failures in a over reactive way. And cutting himself off from the force is exactly what he would do after a mistake like that