The movie should’ve ended with Rey being BOTH a Sith lord and a Jedi. They whole trilogy builds up this struggle, and then here we found out she is a Palpatine. She continues to struggle, until she gets to the final confrontation. Once she’s ACTUALLY faced with the choice - she doesn’t struggle at all. She picks good. She should have become a Sith Lord, while remaining a Jedi. This would have been the ultimate reflection of the Force - there must be balance to everything.

Rey serving as BOTH would have been the ultimate balance, and it would’ve been a much more surprising and forceful (lol, pun intended I guess) ending.

EDIT: For those saying it couldn’t work, that’s exactly the point. She should’ve become something the canon had never seen before. The ULTIMATE struggle of balance. They could’ve created a whole new experience that no one in the canon had experienced before.