Luke’s story - why did he have to almost murder Kylo? Luke was the embodiment of hope - having him finally FAIL his family would be acceptable as his breaking point, but almost a murderer in cold blood of his family? He let the emperor torture him trying to save his father. Those actions are polar opposites - I cannot accept that portrayal of Luke considering his past.
I did initially think that Luke igniting his lightsaber to murder his nephew in his sleep was out of character for Luke. However, we may then consider the emotional poisons that can drive someone to extremes that border on madness.
I considered the afflictive emotions from each of the three intelligence centers of a human being: the Gut, the Heart, and the Head. Rage originates from the Gut when our personal boundaries are violated. Vanity and shame originate from the Heart. Fear and anxiety originate from the Head.
Luke stated to Rey that, in the past, he had no fear of the power that his students displayed, including the extraordinary level of power that Ben Solo had. Murdering someone in his sleep is ostensibly a cowardly act, but fear was not a factor. In his conversation with Rey, Luke speaks of hubris
– both of which are afflictions of the Heart. Luke had an emotional investment in Ben and took things personally when Ben betrayed him.
I can imagine a Jedi defending prostitutes in a bordello, only to later Force-choke his own lover and ignite a lightsaber, when he finds her in bed with another man. That Jedi had no emotional investment in the prostitutes; he did have an emotional investment in his lover.
Similarly, Luke had an emotional investment in his nephew. He took things personally when he was betrayed. I can imagine Luke thinking: “I made you the heir to everything I have. And I find you in bed with Snoke?!”
Time. Hardly any time passed, so there was no opportunity for training - Rey has less than 18 hours of training with Luke. Why couldn’t you let the Resistance escape the First Order and then get caught on Crait trying to regroup after a month or so? Give Rey time with Luke - at the very least time to get annoyed with him. Not a single DAY. It just continues her story as being too powerful, too flat of a hero.
It would have been nice to give Rey the equivalent of several years of training. There could have been a part of the sacred island where the Force causes time to pass at a very different rate. But the movie was long enough as is, with quite a few scenes deleted. Rey’s training would need to be shown as flashbacks in another movie.