No one is saying that he should be the exact same, but that's not an excuse to change the character to the point where he's almost unrecognizable. To write for a beloved franchise like this is a privilege, and to change a beloved character to one that fans don't like any more (and feel more relief than sadness when he dies) is an abuse of that privilege.
In what way? What is Luke about during the OT and what makes him unrecognizable that was not demonstrated in TLJ and can be understood as perfectly plausible after 30 years of time? He became a legend, began to believe the legend and in his hubris built a temple, then when the warning signs for Ben Solo started coming he seemed to not take any mind to them until they became so frequent that he felt the need to look into his mind and actually see what the future of Ben Solo would hold. Right up to that point I do not see where Luke is out of character, so the only thing you really can argue is if Luke Skywalker after seeing what he saw could make an irrational mistake out of instinct and emotion. And considering he has done that very same thing in the past it should be plausible that he could do so again.
may not need adequate on-screen justification to accept Luke's transformation, because you're willing to imagine your own satisfactory explanations, but others do. It's not good writing if the audience has to speculate to make sense of what the writer failed to.
The on screen justification is there, it just isn't spelled out for you. No, you should not need everything spelled out to you in the film for you to be able to understand what is going on.
Haven't you noticed everything that I am saying to "explain" why it isn't necessarily out of character for Luke to do what he did comes from the movies?
What do you dispute about Luke's character out of these things in the movie? These are after the events of ESB which I think is the best place to start.
1. He is incredibly cocky and sure of his abilities in Jabba's palace.
2. He is very defensive of his friends which is why he goes to such great lengths to save Han.
3. He gives himself up to Darth Vader, and despite wanting to turn him back to the light side initiates the confrontation between the two by attacking Palpatine as he wanted.
4. He eventually refuses to fight Vader, but is goaded into attacking him (and trying to kill him) based on an emotional response from Vader threatening to corrupt his sister.
5. Through this lapse of judgement Luke weakens Vader and cuts his hand off, potentially a major contributor to his eventual death by Palpatine soon after.
6. Luke realizes what he has done and stops, but not after the damage was done.
7. He takes Vader's body to be cremated on Endor and the Rebellion is victorious.
8. He becomes a legend (his testimony).
9. Through his hubris he builds a temple believing he can rebuild the order (his testimony).
10. He begins to train a dozen young boys, Ben Solo among them.
11. Through training he notices the darkness building within Ben (his testimony).
12. Eventually it comes to the point where Luke feels he needs to actually peer into his mind (this can be reasonbly inferred)
13. He sees everything and everyone he loved destroyed. While we do not know exactly how this works (which is basically the case for anything force related) we can believe he is telling the truth as far as what he did actually being an accurate projection into his future (unless you want to argue him as being an unreliable narrator in this specific instance).
14. Through the pain he sees for those he cares about he becomes incredibly emotional and distraught.
15. Through his emotional distress he instinctively reacts, treating Ben as an enemy like he did Vader when he attacked him in ROTJ (I do not believe you can just turn off certain aspects of who you are just because you went through them before or over the course of time. Some things just stick with you).
16. He immediately stops himself, ashamed of his response.
17. Ben sees what he sees and it is now too late for any potential redemption.
18. Luke wakes up after being covered in rubble and left to die, sees his temple destroyed and many of his pupils killed because of his mistake.
19. Through his failure and feeling directly responsible for making Ben's future come true, he cuts himself off from the force and becomes a recluse.
I think of these 19 is the closest to being out of character, but I can still accept that as a plausible thing (and probably the best way to explain why Luke was on an island in hiding in the first place).
