The problem with leaving in “I am all the Sith!” is that Rey’s new “I’m a Jedi!” response has to specifically be to Sheevie’s “a SCAVENGER GIRL is no match for the power in me!” statement, right? (edit: just as the poster above said!) Perhaps swapping Palpatine’s lines would work. Here’s a crude mockup of that idea (forgive the unpolished audio and lack of ghosts).
Edit: Does Rey ever refer to herself as a Jedi before this? I know Luke does, but I think that’s alright. It’s just that for this to land well, I think it has to be a ‘breakthrough’ in her confidence in herself, overcoming that self-doubt (which would be undermined if she’d previously considered herself a Jedi).
I’ve been sort of silently watching these thinking “man, I wish it worked, but it just doesn’t.” But I think this arrangement here actually does it.