Luke and Leia being related is just as embarrassing as Rey Palpatine. Okay, well technically not as much since it didn’t contradict the last film, but the idea is just as cringey.
The Luke/Leia thing is infinitely worse than Rey Palpatine. Firstly Luke clearly had romantic feelings for Leia in eps 4 and 5. Secondly there was nothing whatsoever to indicate she was a Force-sensitive Skywalker all along. Thirdly it contradicts Yoda’s entire “too old to begin the training” thing since Leia hadn’t had a lick of training when he announced the ‘other’. And finally, the most overlooked one, Leia was a prisoner on Cloud City when Yoda said “there is another” - immediately after stating a) “now matters are worse” (meaning he couldn’t have known Luke or Leia would survive the Bespin fiasco) and b) he had just insisted Luke sacrifice Han and Leia for the greater good!
Rey’s being a Palpatine at least made some sense of the fact that she had godlike powers for no good reason.