The thing about the insecurity of Rey being a worthier Sith heir wouldn’t land with either Kylo Ren or the audience given that as far as he and we are concerned, at this point of the story the Emperor just wants to have her killed. The drama is that instead of doing that he’s planning on having her side with him. It is not revealed till later that Palpatine wants her as the heir. Therefore I think leaning into that at this point of the story is a bit premature.
Sorry, but I’m not sure you fully understand what JJB’s goals are here. The whole “Palpatine pretends to want Rey dead but secretly wants her to join him” thing is completely gone, or at least heavily altered. Palpatine’s end goal here, seemingly stated offscreen in the part of his conversation with Kylo that we didn’t see, is for Rey and Kylo to fight each other to the death, so the one who survives can take his throne. Vader saying “you are unworthy” is intended to prey on Kylo’s insecurity over his defeat at Rey’s hands in TFA, implying that Kylo won’t be strong enough to kill Rey and become Palpatine’s true heir.