That is totally not what I took from the movie. It seems like you’re taking a super depressing message whereas I see a really hopeful one. Unless I’m misinterpreting you. Our failures and mistakes make us think we aren’t capable of becoming who we want to be, but if we continue to believe in ourselves we can overcome our failures and eventually become who we want to be. Luke doesn’t think he is the legend people believe in, but in the end he once again believes in himself and truly becomes that legend. In TLJ, the legend has both tangible and symbolic value.
The way you describe Lucas’ work is exactly what happens in RJ’s work. Luke overcomes his flaws and reaches a state of enlightenment.
The reason I’m more inclined to go for the depressing message is, that I find much of what I have seen depressing. The heroes of the OT lived to see all that they fought for destroyed. Han and Leia’s relationship dissolved, while their son became a homicidal maniac, who ultimately murdered his father, Luke saw his Jedi academy destroyed, and abandoned his friends, and the galaxy at large, the New Republic was wiped out in an instant, once again forcing the good guys in the role of an even smaller rebellion. To me Luke finding a shred of dignity, and some hope that the next generation may make things right for a while cannot compensate for the depressing notion, that some evil force can just be pulled from behind the curtain to push the reset button without explanation. The real hope for me is that TROS will provide some much needed context to help me believe our heroes can finally break this rather cynical and depressing cycle.