I think I have a rough idea of how to streamline the ending and even have it be thematically more powerful. First, remove the whole death ritual angle. This way, Palpatine is not asking Rey to kill him, but rather offering her a deal similar to what he offered Kylo at the beginning of the film, except in this case he is inviting her to rule as grandfather and granddaughter. This is more compelling to Rey for two reasons: 1) It seems as though Palpatine may be sincerely reaching out to her as family, and offering her something that would make her more than a “nobody”, i.e., a “birthright”, and 2) whereas Rey initially wanted to “destroy” Palpatine for killing her parents, Luke’s pep talk actually softened her up and helped her dial down her anger/hatred. So now she is going to face Palpatine, but is completely thrown off kilter by his proposal and no longer sure she wants to kill him. He is offering her everything she ever wanted after all, i.e., family and a sense of identity. Having said all that, Palpatine is really only trying to buy time until Kylo arrives so he can draw strength from their Dyad. This is because he’s presumably quite weak, and Rey could realistically defeat him in his infeebled state. Rey ultimately rejects his proposal of course, but at least in this way, it could be a little bit tempting for her. However as soon as Kylo/Ben arrives, Palpatine immediately turns on her, because he no longer needs to buy time. And so he gets to work sapping their energy. I think this ending is much better, because in this case, at least Rey is offered a more difficult choice, i.e., a sense of belonging and identity with her grandfather, or a lonely life as the last remaining jedi. Of course, after her trial of faith so to speak, the Jedi come through for her, proving that they can also provide that sense of belonging and identity.
So this is how it might work with the death ritual removed:
Palpatine: I never wanted you dead, I wanted you here. Empress Palpatine, you will take the thrown. It is your birthright.
Rey: I haven’t come to lead the Sith, I’ve come to end them.
Palpatine: Your hatred. Your anger. You want to kill me.
(remove line about him wanting the same thing. Remove any dialogue urging her to kill him.)
Rey: All you want is for me to hate, but I won’t, not even you.
Palpatine: Luke was saved by his father. The only family you have here, is me.
Palpatine: No one is coming to help your friends. Take the throne. …Only you have the power to save your friends.
(This is where Rey Force transfers the lightsaber to Ben and the fighting ensues)
Palpatine: You are nothing. A scavenger girl… (granted, this line would have to be moved from later in the scene, and may not be possible, but it isnt essential to do so either).
Palpatine: Stand together, die together…(etc., etc.,)
I feel like the shot where Palpatine throws Ben off the cliff could easily be removed. It would be one less annoying fake out, which this movie is full of. However, that is neither here nor there.
Other lines from earlier in the film could be removed as well, such as Palpatine telling Kylo: “Kill me and my spirit will pass into you, as all the Sith live in me.” This line wouldn’t be necessary since it wouldn’t factor in later in the film. Another line that could be trimmed would be where Kylo says to Rey: “What Palpatine doesn’t know, is that we’re a Dyad in the Force.” The first half about Palpatine not knowing could be removed, retaining the useful bit of information in the second half. Again, I just think it’s really implausible, if Palpatine has been manipulating Kylo all this time, that he doesn’t know about the Dyad, and doesn’t have plans to exploit it.