I don’t know if we should be outright denying the story at this point. After all, if we cast too much doubt on Palpatine’s story, we rob it of its power right when it should be paying dividends. Ideally, we would need more thematic reason for the existence of this ruse in the film, more than just a machination of Palpatine. So how about tying it into Leia’s journey?

“What are you most afraid of?”
“Myself.”
“Because you’re a Palpatine? Leia struggled with that same fear.”
“She didn’t tell me…she still trained me.”
“Because she saw your spirit…your heart.”

…

“She was quick to learn in our training. But she feared our family’s darkness within her. She surrendered her saber to me and said that someday it would be picked up again…by someone who would face that darkness, and overcome it.”

…

This way Luke isn’t denying the story, but rather recontextualizing it in a way that makes Leia’s story more impactful. After all, Leia says to Rey ‘Never be afraid of who you are.’ This fear of identity is a part of Leia’s character in the film, and if it’s not for Rey’s benefit, then it should reveal the sort of fear that Leia may still struggle with.

If we make this the reason Leia surrendered her saber, it also gives us a strong hint that Leia believed that her son would have been the one to take up her saber and overcome her family’s dark past. And indeed Ben eventually does triumph in the end, but she couldn’t have realized that Rey would be the one to take up the sword, a girl from nowhere that became the daughter she never had.

And so, Rey can now complete Leia’s incomplete Jedi path in a very literal way that wouldn’t be possible without Rey Palpatine, justifying its existence in the story.