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).
I’ll add to the chorus that I think this one works great! The reordering of the lines flows perfectly. My only concern with changing this line before was that the “all the Jedi” line is tied to the theme of “coming together”, however with the phantom four I guess it’s fine if this is actually shown rather than told, Palpatine says he is all the Sith yet he stands alone, Rey only says she is a Jedi yet all the Jedi stand figuratively and literally behind her. I think it works and it’s worth it just to remove that Endgame “I am Ironman” moment, plus Rey feeling worthy of calling herself a Jedi is a nicer and more explicit payoff to her struggle in the film.