Ok, so I tell myself I'm not going to engage in these arguments, because I'm not going to change anybody's mind. But, as someone who enjoyed what they did with Luke in the TLJ, you see this stuff a lot. So, my two cents:
I agree that what happened at Luke's academy had a far greater impact on Luke than Vader ever did. People say that's hypocrisy, but it really isn't. @fireproof78 laid out a lot of good thinking on this subject, and I'll defer to his explanation in large part, because it echoes my own.
However, one point that isn't raised about Luke's journey in the discussion I'm seeing here is integral to The Last Jedi, and Luke's place in the larger thematic exploration. And I apologize, a lot of this is rough thought that I'm just putting into words for the first time. So if it isn't clear, or well organized, sue me.
In the OT, we learn the basics of the light side vs. the dark side. And we're very clearly presented with Luke's choice in RotJ, where he rejects the path offered him by Yoda and Obi-wan and finds a better way. We, as an audience, feel how correct Luke's choice is, and we see that he is correct when he succeeds in redeeming Anakin, but the movie never dwells on the why. Why is Luke's choice the right one, not in terms of the audience and the emotional reaction, but in terms of the Force? And if Luke's was the right answer, why were Yoda and Obi-wan wrong? There's a ton of fascinating subtext, particularly in the PT, but it's never put into words.
The answer is finally put clearly into words in the TLJ. The Dark side destroys what it hates, or fears. The Light protects what it loves.
Without getting into an essay on the topic, this is why Vader could be redeemed. This is why Luke's choice in RotJ is correct. This is why the Jedi and the Old Republic fell, and why darkness had already consumed the Jedi Order before Palpatine ever put his plan into motion. It's why Obi-wan can't bring himself to kill Vader on Mustafar. It's why Kylo Ren has issues. And it's why Luke ends up where he does in TLJ.
Yes. Correct. 100%. And yet Luke faltered. (We'll ignore for the moment how you seem unable to forgive him for that, and what that says in terms of your own argument.)
Luke wavered with Ben. He saw darkness and he reached for violence to combat it. And what Luke carries with him isn't just shame, or the crushing weight of failure, as fireproof78 laid out. All of that is true. But he also carries darkness. Born of an almost primal reaction to a threat, but born of darkness all the same. When faced with the darkness rising in Ben, Luke wanted to destroy it.
And that darkness is what lingers in him after Ben turns on him. In his failure, he runs away. To hide, and stew, and think about the end of the Jedi. His attachments, if you want to look at it comparison to his father. All of it, every word, every action, are influenced by the dark side. Luke hasn't fallen like his father did, but he's being manipulated in the same way Yoda and Obi-wan were. Away from the truth, and hope and love, and towards something else.
Rey finally gets him to open himself back up to the Force, and to the galaxy. And in so doing Luke finds the place inside himself that simply knows what is right. I think Luke is attuned to the light in a really interesting way in those moments. He feels the truth of it, instinctively, without necessarily being able to put it into words. It's why he choose to try and save his father. And it's what brings him back from the edge during the final duel with Vader, when he's nearly gone dark. When he "goes" to Crait, Luke is done being a teacher, or an uncle, or a hero or a failure. Luke is finally once again being a Jedi. Maybe the first true Jedi in a really, really long time.
I don't think anybody but Luke could have taken that journey, or made it meaningful. It's both the completion of an arc that began for the Jedi in the PT, and which culminates in Luke's victory over the Emperor in RotJ. It's a metaphysical battle, one which darkness was winning from the beginning of the PT, and which now, finally, after Luke's actions first in RotJ and again in TLJ may have turned in light's favor.
