I like the vast majority of that, JJB. I think it’s focused and clean. I’m on the fence about Rey’s force awakening bringing her to the attention of Palpatine, but i don’t think we need the idea that the two need to fight to see who’s best. Rey’s the preferred host, so once she’s available to Palpatine, he’s more interested. (Implicitly, if you like, Kylo’s less innately powerful because he’s third generation.)
The idea behind that is he would be convinced Rey is his strongest heir, anyway. The only reason it needs to be worded that way is because we’re trying to reconcile the idea that he initially wanted Rey dead in this movie with the idea of her being his preferred candidate the whole time. So think of it like this, he wouldn’t tell Kylo - “Hey bud, I need you to go get yourself killed by Rey so she can tap into the dark side again.” He’d say what he told him as motivation - “Go on and try to kill her, end the Jedi, and maybe you have a chance of being what Vader could not be (Offscreen: but I doubt it, in all likelihood my chosen heir Rey is going to kill you in anger, so I win either way here).”
The reason he’d say “The princess of Alderaan has disrupted my plan” is because he intended for Kylo’s death to cement Rey in the dark side, but instead Rey healed him and Ben returned.
EDIT: Alternatively, I could make this idea that he wants Rey more apparent and have Kylo’s role as a failsafe less apparent - “I know Palpatine only wants me to try and kill you so that you give in to the dark side.” But this just raises questions about how he knows Rey is his “chosen heir” over himself to begin with.