Edit: I just watched the scene again and I’m so annoyed at how Luke completely forgets everything he learned about internal conflict by saving his father and Rey spoon-feeds this wisdom to him like she’s the Jedi master. Ugh.
I’ve found it helpful to look at Kylo and Rey as being written to represent Star Wars fans. Rey represents those who are avid and hopeful fans of the franchise, who know everything about the Jedi and what the ‘real’ Luke would do. This is why she’s so disappointed in what he’s become.
Kylo represents the fan who is tired of the whole dichotomy between good and evil, rebels and Empire, and wants to make the franchise about something else.
This is a big reason why it’s so hard to take these movies seriously - the stories aren’t written as a natural progression of events but more as a meta commentary on Star Wars itself.