Trim Kylo’s line to “You’re Palpatine.” (and similarly adjust Luke’s to “Because you’re Palpatine.”).
Rey has to come to terms with discovering she was, in fact, Palpatine this whole time. This allows the movie to explore challenging moral questions like “Does being an evil person make you an evil person?”.
The guy on Exegol is just some faker; that’s why Rey - the real Palpatine - blows him up.