The point is that Rey had a terrible upbringing with unimportant, awful parents who left her alone in the middle of no where, yet still managed to be a good person and a hero who is worthy of legend.
That point is contrasted by a villain that had a good upbringing with a good family and an incredible lineage and still managed to be an awful piece of shit who refuses to be a good person, even when the choice is given to him in a manner that would require him to make up for none of his past crimes.
If that goes over your head so much to where you’re convinced the story can’t make sense without Rey coming from some bullshit idea lineage, I don’t know what to tell you.
Everyone who worked on the film has a Carrie story, but the sweetest and most heartbreaking one belongs to Isaac:
“One of my favorite things that would happen from time to time on set would be when Carrie would sing old songs,” he says. “Whenever that would happen I would offer her my hand and we would waltz around the set – on a starship, in a Rebel base, on an alien planet, and she would sing and we would dance. So surreal and beautiful to think about now. For all of her delicious, wicked humor and fiery energy she also had such sweet grace. I miss her dearly.”
Beltainefaerie's Flights of Fancy 