Personal opinion blah, blah, blah.
Rae is nothing but a Mary Sue. She just knows how to fly ships with no experiance besides working on it. She apperantly can figure out whats up with a ship before Han Solo (The single most badass none force user in the movies) who would know exactly what is wrong with his ship before she should. Lets not even mention the Force BS. It took Luke presumably months of training and actual experiance (Him looking for Han and Leia) to become a proper Jedi. And he only one against Vader because he used hos angry and tapped into the Dark Side.
She somehow resists a trained Force User (a incrediably powerful one at that and one thats park fucking Skywalker) somehow. Somehow just knows how to mess with minds. And in the last fight, somehow just melds with the Force.
Fin is a underdeveloped character. A Stormtrooper, kidnapped and raised to know nothing but war. Beaten and tortured into submission, yet he still hangs onto some semblance of a personality. Not to mention he was a fucking Janitor? Why send him into any form of battle. So instead of having him struggle between whats been beaten into him? He is fine and happy and giddy as he blasts presumably a good portion of friends. Then from then on out he is a bumbling idiot there for comic relief. They show some semblance of character development when he tries to tuck tail and run, leaving Rae behind to presumably go fight and die.
But as soon as something might happen to her he is a lost puppy.
Not to mention they are shoe horning his character into being a political tokeb just cuz.
I could go on.