The whole legend/messiah/hermit routine was done really well in the Dune novels IMO. It’s a similar scenario (maybe Rian’s a fan?) where Paul’s prescience/power comes to a standstill and he wanders off into the desert to die. He survives of course, and becomes this ragged preacher who rails against the current regime from the sidelines, challenging his own legend as he does so.
The difference is Frank Herbert still manages to maintain the dignity of the character. I’m a big fan of the Gary Kurtz ‘disillusioned Luke wandering off into the sunset’ idea, but it comes with the caveat that Luke not become pathetic. Since I find ROTJ to be disappointingly dumbed-down (after the brilliantly nuanced TESB), I still cling to the notion of Luke rejecting the binary view of the Force shared by his mentors, and seeking a new path.
This is what TLJ should have been IMO. Not Luke ‘giving up’, but Luke rejecting the notion of Jedi orthodoxy. Perhaps he and Kylo could have shared a vision where death to one of them was revealed as the only outcome. Kylo embraces the vision (in his lust for power and the restoration of his grandfather’s evil legacy) and Luke rejects it because he’s sick of this ‘Dark Side/Light Side’ business and doesn’t want to kill his sister’s son. His not training Rey could be a ruse, a deliberate way of setting her on a new path free of the old Jedi constraints. When Yoda appears in TLJ, Luke reveals the ruse - that the old ways are gone now - and then does the Force-skype with Kylo. This would be a way of restoring the legend, setting a new agenda as well as a new ethical framework for Star Wars (there is no Dark Side, only the choices we make), and kickstarting a new type of Jedi.
I mean this essentially what the film was doing, but I don’t believe we needed to have Luke stand over Kylo with murderous (however fleeting) intent, or revert Luke to pre-ROTJ status with Yoda repeating the “always looking to the horizon” lecture. Luke’s ‘looking to the horizon’ was his strength. This movie should have, and could have, reinforced this.