Confirmed, Rey is and always was a Mary Sue (spoilers)
There is no other current writing term in existence to describe such a character; that is constantly the center of attention (spotlight stealing), completely overpowered and highly skilled without a backstory to justify it, extremely and inexplicably noble (to a degree that is unbelievable), immediately loved, respected and revered by the other characters to a point it overshadows other character including the established ones.
It does not matter that she is a 'Palpatine', that is not by itself a sufficient explanation for her remarkable way of just acquiring force powers when the plot calls for it, Palpatine had a master and trained for dozens of years. She never struggled to over come anything; does anyone even care that she is fighting Kylo multiple times in this movie when she has been making him look pathetic since the first movie. I was glad he finally 'beats' her in a fight (only to get freaking stabbed through the check by her a few seconds later) but it was too late to give it any real impact, and she still freaking stabs him which immediately negates his victory. Can't have the Mary Sue ever lose in any kind of substantial way now could they.
If they wanted to go with her being so powerful she becomes arrogant and out of control they needed to start it with the 2nd movie. If they wanted to show she needed to train to develope her full powers, it should have started in the 1st and continued in the 2nd. It is too little too late now.
They even have her die sacrificing herself (another characteristic of the Mary Sue trope). Only Rey is a special kind of Mary Sue so she can't stay dead, she has to be brought back so she can 'identify' as a Skywalker. I think I hate the Rey defense since 2015 even more now.