So you, Jake, finally read my actual defense itself.
The self-worth stuff is not really headcanon, it’s actually inferable from the movies. Yes, it relies on inference, like almost everything else in this trilogy.
It isn’t that Rey wants to be important in the grand scheme of things and in the galaxy and make a difference for the sake of it, blah blah blah, yadda yadda. It’s that Rey wants to feel worth something to other people, she wants people to give her validation and appreciation so it’d essentially, emotionally push away her feelings of self-worthless so she can feel happy - but it doesn’t address the core belief itself, only its effects.
And she wants to feel worth something to her parents, as well - after all, they were the ones who abandoned her. Parents are supposed to care for you, love you, take care of you, not consider you to be worthless.
Also, Rey doesn’t technically want to be great, because she feels unworthy/undeserving - her feelings of unworthiness are a symptom/piece of evidence for her core belief of self-worthlessness. She rejects the Skywalker lightsaber that literally called out to her when Maz offers it to her because she doesn’t feel worthy of it. She keeps relying on other people (i.e. Luke, Ben) to be the Hero when she doesn’t want to do it herself.
Even when she does become the Hero it doesn’t imply she’s found her own importance, it’s that she has no other choice but to be that Hero, and even in The Rise of Skywalker she doesn’t feel worthy or deserving of being that Hero (“I will earn your brother’s saber…”) because she thinks she’ll turn to the dark side and no one’ll give her validation and other people will consider her to be worthless. The same happens in The Force Awakens - just because she’s using the Skywalker lightsaber in her fight with Kylo Ren on Starkiller doesn’t mean she finally felt worthy of using that saber, just meant that she has no other choice but to use it.
The truth Rey comes to terms with in The Last Jedi is not that she has to rely on herself, but that her parents really did throw her away like garbage and consider her to be worthless. She finally moves on from her shitty parents, and now relies on other people aside from Luke, Han, Kylo Ren and her actual parents for validation. She says “They were nobody” in the sense that because they weren’t important, it meant they had no actual reason to abandon Rey - something I address in the defense itself.
I do agree with you that the “Rey Palpatine” stuff is similar to Luke’s arc, but it’s simply a natural way of reinforcing her core belief of self-worthlessness - in the same way, Jakku being a desert planet is a way of visualizing the hell Rey’s gone through during her time on Jakku, and Starkiller Base is a way of saying that the First Order’s an improvement over the old Empire (hell, even the laser splits into five beams whereas the Death Star’s beam didn’t in A New Hope when it destroys Alderaan).
This is a really long way of saying “it’s not really about what the person who wrote the story says it was about!”
We all interpret and view art differently (not that film quality is subjective). Lucas said that the saga was about Anakin when he was still in charge, but now with Disney in charge it’s about the whole Skywalker family.
Lucas’ POV: The prequels are the fall of Anakin, and the originals are his redemption.
Disney’s saga… and its unintentional meaning: The prequels are the Skywalkers’ origin story, the originals are their rise, and the sequels are how their legacy would live on once the actual Skywalker bloodline dies off.
Stories unintentionally convey unintentional meaning all the time, if you know what I mean. It doesn’t really matter as to what the creators themselves say, because inferences and what is shown and told to us in the film itself conveys otherwise.