The message of Luke appearing in projection form isn’t that “the Jedi are good, actually,” it’s that image is everything. The real Luke doesn’t matter, because the specter of younger, popular Luke is what people like. It’s all about deception and propaganda. The actual Jedi and the actual Luke sucked but they’re a noble lie.
I mean, that’s going a bit too far I think. The movie clearly at least tries to end on a positive note, emphasizing that Luke’s heroic actions on Crate (Krait?) served as inspiration for a potential new generation of Jedi, beginning with ordinary people all over the Galaxy, like the famous “Broom Boy”. Clearly, the ending was supposed to be uplifting and positive, promising that the Jedi would rise again - in some form or another.
I think this ending is stupid. It pretty much killed my interest in the Sequel Trilogy. The whole movie is mostly stupid. But I can at least discern that the director at least wanted the ending to be perceived as hopeful and positive, but also bittersweet, like the ending to Empire Strikes Back.