Yeah, basically, the only way Palpatine’s plan has any logic is if getting Rey and/or Kylo there helps his cause.
The problem is that Kylo already voluntarily went there at the start, demonstrating Palpatine doesn’t actually NEED Kylo.
So for the climax requiring Rey’s presence, it would need to be either:
Palpatine specifically needs her there for the soul/genetic transfer. This was basically what the movie suggested as is, though in an incredibly hamfisted manner since why would she willingly be possessed by Palpatine after he says that’s what he’s going to do?
Rey and Kylo’s force bond (the Dyad) is what Palpatine needed. This could fit with Rogueleader’s idea–in other words, Rey IS NOT Palpatine’s granddaughter and it’s their emotional bond that gives him strength. It fits with the “Rey is nobody” theme better than the weak “it was just her parents who were nobody” excuse. I realize this isn’t the best explanation, but we have to work with what the film gave us.
Honestly, the Palpatine-Rey connection is the weakest part of her story since his plot makes no sense. If he HAD NOT told her that striking him down would result in him possessing her, she probably would have done it in anger and he’d have won. So why did JJ have Palps monologue like that?