Going to backtrack a statement I made in an old Star Wars: The Force Awakens post. Rey Skywalker is definitely not a Mary Sue:
7. She cobbled together a computer from crashed ships and found a data chip with a functioning flight simulator program. She used the program in her spare time, like when she was trapped by the storm, and gained experience navigating a number of different ships.
8. She recognized violence was part of living on Jakku and learned to defend herself. She had to participate in so many fights over the years she can’t remember the exact number.
So she didn’t “just learn” how to pilot. On a desert planet with nothing else to do besides scavenge and (barely) eat, anything to break the monotony would be seized upon, hence her learning of mechanics and piloting. It makes sense she would be extra ambitious if she ever wanted to build some sort of ship to leave, right?
She also didn’t “just learn” the Force when she was able to resist Kylo Ren’s Force mind probing during interrogation. Ren is powerful, but Rey didn’t have a pampered disposition, so she had developed the mental fortitude of living in a sandy hell like Jakku to be able to fight back when Ren tried to pry secrets.
With all this, Rey isn’t half the Mary Sue (Marty Stu) Anakin was. A champion podracer at 9 year old?