Sorry, but this is just not true. The entire premise of TLJ is, that Luke has seen the suffering Kylo would cause in his vision. He knew exactly what might happen, but ultimately he did nothing to stop it.
Ah, but Luke never says what Kylo would do, only that he was already full of darkness and would do bad things. What he saw he does not elaborate on. For the purposes of what you are saying, we can assume he did not see the galaxy wide distress Kylo would cause.
So, realistic portrayal of toppling a despotic regime, realistic portrayal of a fallen hero, and a realistic portrayal of a character based on actual psychology and the given traits of the character (I checked up on that with some people who know these things), and you have a very realistic setting for the ST to take place in.
Again Star Wars is not realistic. The hero’s journey and myths are not realistic. They are not meant to be.
And yet GL used many things that lends realism to the stories. Not of course the technology or the force, but in the way the people act. He had just come off of American Graffiti and Star Wars has many of the same feelings to it that are grounded in reality. I think that is why even though the story and character archetypes are based on mythology, they feel relatable and grounded. You may have gone to class with Luke, Leia, or Han, had a teacher like Ben or Yoda, or a friend like Lando. While the story is based on mythology, the people come of as real in a fantastic setting.
No, it is not the story you wanted, but it is not flawed in the way you describe it. It is flawed from your view because you see Luke as a legendary hero and that the heroes of the OT should not have failed like they have in the years between the OT and ST.
Luke was a legendary hero, as follows from the hero’s journey. It’s not what I wanted, it is the way it was. That was allways the intent. His story was supposed to end in ROTJ. Of course then Lucas decided to sell his company, and there had to be a ST with the classic characters, and so they had to somehow extend the story. The ST has unrevalled the mythology of the OT in order to do this. Some will like this approach, and others won’t. I will allways prefer the myth, but I like the more realistic approach of the ST enough to want to see, how it plays out.
Luke went on a Hero’s journey, but that does not mean he has to stay a hero. When you think about it, TLJ repeats the offer of a Hero’s journey to Luke, and like the first time, he rejects it (“I can’t come with you to Alederaan. I have to get home.”). And like the first time, he gets a second chance and takes it. But his archetype in this film is not the hero, but the mentor. He rejects the role as mentor initially and then his mentor shows up and makes him see the error of his ways and then he accepts and sacrifices himself for the cause.
Luke is no longer the hero. He was not the hero when he took on students. Luke made a fantastic hero but thinks he failed being a mentor and is unwilling initially to do it again, especially when Rey turns out to be as powerful as Ben Solo was. We still don’t know if he actually changed his mind or decided to play the hero again one last time. Luke showing up as a force ghost in IX would mean he decided to become the mentor.
It all fits with the hero’s journey with our old hero becoming the new mentor. But rather than the type of wise sage we see in Kenobi, we get one beaten down and unwilling to teach and the few lessons he offers are basic and incomplete. So our Hero Luke has become Mentor Luke and in his first try at it he failed and now he fears creating another Kylo Ren more than what Kylo Ren might do. Typical rash Luke saw the darkness of Kylo but probably not all the ramifications of how he would help Snoke and the First Order.