The Luke complaints in my opinion are unrealistic. Do you think a human being is incapable of making a mistake like Luke did? The whole point of the film is that no one, even a legend, is incapable of mistakes. Someone as great as Obi Wan failed with Anakin. Not a huge stretch of the imagination to me.
I’m focusing on this because to me, the main story of this film centers around this flashback between Kylo and Luke. The reason I think the Luke complaints are valid are because it’s absolutely beyond me to think Luke went from the leap of, “Kylo is having dark thoughts” to "I need to kill him RIGHT NOW!"
Luke over the course of three films learned something super important: patience. Luke started out impulsive and impatient, but in ROTJ, he is calm and collected, more wiser. So why in the world is Luke all of a sudden this trigger-saber-happy Jedi master? I’m not even saying Luke should be flawless. I was going to accept that Luke just sucks as a teacher and messed up Kylo’s training. But instead, his mistake was… being impulsive? Yeah yeah, Luke finally felt shame at the last moment, but my goodness, I can’t even fathom Luke’s first option was to march to Kylo’s room, ready to strike with his ignited saber. As far as we know, Kylo hadn’t even done anything bad beyond just having dark thoughts. Luke should be so much wiser to deal with this kind of stuff because he himself did feel the tempt of the darkside in ROTJ, something that Obi-Wan never did and hence why Luke was miles better than most Jedi before him. Luke should be the best person to help Kylo work through it. And fine, if not, Luke should had been figuring options A, B, and C, diving deeper into the mysteries of the Force in an attempt to bring Kylo back to the light. Instead he follows the same exact path of Yoda, which should had been a lesson in of itself to begin with to NOT DO.
This is why I think the complaints are warranted.