Just like you're trying to extrapolate the significance of her gender while I discuss the force and how I find it can take an interesting narrative if the trilogy showcases a person mastering both the Light and Dark side in a movie called "Star Wars"?
The association between women and darkness/evil is
not something that I've extrapolated; it's something that's been present in religion, philosophy, literature, art, and society since ancient times and that has consequently led to women being considered subordinate, as holding lesser positions of prestige in society compared to men, as deviant compared to men who are paragons of what it means to be human.
http://www.friesian.com/gender.htm
Beginning with the proposition that Luke (the traditional male hero archetype) was already established as a good, upright, and virtuous hero in the OT, having Rey do anything but live up to his legacy - and she's already doing so in her own, perhaps even more poignant way - would repeat this pattern all over again (she would then fit the archetype of the deviant woman who needs to be redeemed) and erase any potential she has to be a symbol of a shift away from that paradigm.
Contrary to being an "interesting narrative," it would be a
completely uninteresting and
sadly predictable narrative.
The better narrative would be to give her different choices than Luke had, which is something we've already seen happen; Luke always had Obi-Wan's words coming down to guide him, while Rey has had to make all her choices based purely on faith. That's a positively astounding shift that makes Rey
an even better Luke than Luke himself was, while forcing her to get there through
more deeply personal struggles and more desperate circumstances.
What's not exciting about that?
Disagree. Leia is great in the OT.
Leia is in constant need of saving by male protagonists, is generally depicted as naggy, and is explicitly sexualized in ROTJ.