The ST doesn’t “retcon” the OT or make it wrong or whatever (ruin it, I guess?). The OT is still the OT and will always be the self contained story that it is and nothing that comes after can change that. But you admit Luke ended his hero’s journey there, so what is the ST supposed to do then? Just preserve Luke in a glass case of “perfect mythic hero”?
The ST does exactly what a sequel should do. In many ways this is very similar to the way Empire re-contextualizes the original Star Wars.
If the story must continue with all new characters, then Luke’s character should’ve just followed the natural progression that the OT set up and taken over the archetypal role as the wise mentor. That is exactly what they originally tried to do as Abrams and Michael Arndt have stated. According to Arndt though, they couldn’t figure out how to do this and not have Luke steal the show from the new “hero”:
“It just felt like every time Luke entered the movie, he just took it over. Suddenly you didn’t care about your main character anymore because, ‘Oh fuck, Luke Skywalker’s here. I want to see what he’s going to do’.” – Michael Arndt
I understand what he’s saying, but on a fundamental level I disagree with that. I don’t see any reason why Luke couldn’t have taken a “backseat” to Rey, during the course of the story. After all, they basically did the exact same thing with an equally popular character in Han Solo.
First, Luke can’t just be Obi-wan v2. Classic performance aside, Obi-wan in the OT was mainly a vehicle for exposition and an introduction for Luke to the way of the force. And that’s okay! And was necessary then. But we already know what the force is, we already know what the Jedi are and what happened in the OT and whatever. Plus, unlike the PT (which turned Obi-wan into a main character after the fact), it’s weird to have three movies with a main character (and not just any main character, basically the main character in modern cinema) and then for him to only be a tertiary character when he shows up again. Obi-wan didn’t need a story in the OT, but Luke needed one in the ST. And to give a character a compelling story, you need to strip away their perfection.
As for Arndt and Abrams thinking that Luke would steal the show, I pretty much agree, and I’d actually submit TLJ as exhibit #1. Even after a film and a half with Rey as our protagonist, once Luke shows up on Crait, it’s the Luke show. Which is awesome but I do think it robs Rey of the power of her climactic moment (lifting the rocks).