He starts out using Luke’s behavior in A New Hope:
I don’t think it’s that far beyond how Luke is presented in the OT. Initially he’s all for killing Vader to avenge his aunt and uncle, Obi-Wan, and his father. When Vader reveals he’s Luke’s father, it allows him to look beyond the “monster in a mask” and see the human underneath. Even Obi-Wan and Yoda urged him to face and strike Vader down in order to become a Jedi Knight, but Luke’s instincts told him different.
For me, that’s the key: Luke has always trusted his instincts. He did so to destroy the Death Star, and does again to face Vader on Bespin rather than complete his training — that one was a mistake in the short term, but it allowed him to realize the truth and ultimately redeem Vader.
He even quotes Obi-Wan Kenobi who tells Luke in Return of the Jedi, “Your insight serves you well.”
He even explains this insight helps him redeem Vader:
Luke’s insight into the truth of Vader helps return Anakin to the light and defeats the Emperor. His insight has served him well at every major decision.
He then goes on to explain Luke’s behavior in The Last Jedi.
Then comes Ben; his own nephew, except when Luke looks at him through the Force — using his feelings, his insight — he sees only darkness. Now, Luke’s trusted instincts are telling him to strike Ben down for the good of the future, in the same way his damaging trip to Bespin was ultimately a good thing, and to ignore the advice of his Jedi Masters and reach out to Vader was a good thing.
He then explains Luke has always trusted his instincts and he does so in The Last Jedi as well.
Luke, of course, realizes his mistake; that his instincts have been clouded, but by then it’s too late. I’d argue that Luke in the flashback does what Luke has always done as a hero of the Rebellion and a Jedi Knight: he trusts his instincts.
And they led him wrong, hence retreating into exile unable to trust his insight any more and in an emotional crisis.
While it’s a nice theory, it’s about all it is. The idea that Luke always trusts his instincts is just plain wrong. In fact, his instincts when he destroys the Death Star are overwhelmed by Obi-Wan Kenobi telling him to trust in the Force, which he does. He actually turns his targeting computer in order to trust in the Force – not his instincts.
Luke’s insight into Vader doesn’t help him redeem him. In fact, it’s the opposite. Luke tries to strike down the Emperor in order to attempt to redeem Vader. Yes, he does try and bring Vader to the Dark Side throughout his battle, but his initial instinct is to strike down Vader. He even goes into a wild rampage and almost kills Vader when he threatens to seduce Leia to the Dark Side.
It is not until Luke hears the whispers of the Dark Side in the Emperor’s taunts that he sees he is losing himself to the Dark Side. He was on the brink of striking down his father and become the Emperor’s new apprentice. But he chooses in that moment he would rather die than fall to the Dark Side. This isn’t insight into Vader, it’s insight into himself.
But Luke does feel the conflict in Vader. He senses there is still good him. But it’s Vader’s choice and Vader’s choice alone.
Vader sees Luke’s sacrifice and makes his own choice in that moment to save his son and kill the Emperor. It has nothing to do with Luke’s instincts. It’s the complete opposite.
Luke doesn’t trust his instincts all the time. In fact, in his most heroic moments he almost never trusts them right off the bat. He has to learn from them and course correct. That’s exactly why his portrayal in The Last Jedi is an abomination.
Unlike Vader, Luke Skywalker wants to remove Ben Solo’s choice. He believe he is a lost cost, there is no good left within him. This is obviously untrue as Rey constantly sees the conflict within Kylo Ren. Director Rian Johnson goes out of his way to show us that conflict when Kylo Ren refuses to kill his mother.
Luke Skywalker would have seen that conflict too and attempted to bring Ben Solo back to the Light Side. Even after he had destroyed the Jedi temple and killed the padawans, he would not have given up. He would have attempted to bring Ben Solo back to the light even if it meant sacrificing his own life. He did it once before, he would do it again especially for his sister and best friend’s son.
Rian Johnson, Disney, and the Lucasfilm Story group if they even have any influence any more have lost sight of who Luke Skywalker was and by extension have lost sight of what Star Wars is. No fan theories can explain the absolute abomination The Last Jedi is when it comes to Star Wars lore and character.