Stuff!
Things!
Excitement!
I'm really happy to see you explain what a Mary Sue actually is. It's... Refreshing.
Now, all that said.
Would you consider Rey as such?
Hmmmmm......
Rey is pretty powerful. She gets captured twice. Without the force she's a pretty average combatant. (So she bo-staved a few thugs and shot a stormtrooper. Haven't we all?.)
From wikipedia:
A Mary Sue is an idealized and seemingly perfect fictional character , a young or low-rank person who saves the day through unrealistic abilities. Often this character is recognized as an author insert or wish-fulfillment. [1] Sometimes the name is reserved only for women, and male Sues are called "Gary Stus" or "Marty Stus"; but more often the name is used for both sexes of offenders.
Is she idealized and perfect? She's a little tough from being a desert not-slave (she gets paid in food), but for the most bit she's made out to be a little naive. She might not be as shocked as a farmboy apon seeing the platitudes of the galaxy, but I don't think she's quite perfect. Perfect skin maybe, but not a "perfect" character.
Low-rank. Young. Yes. Yes. Moving on.
Author-insert, or wish fulfillment? I don't know the author well enough to say. Wish fulfillment? She's not as leathered as Shimi, but she's hardly the first toughened desert-girl we've run into. She's not the same type of girl as Leia, and I'm not sure if anyone upper-class is going to become a character any time soon in this political climate. It's really hard to say here.
I think the Mary-sue paranoia comes from some of the stuff they've been doing recently with female characters. Popular opinions drive the content of stories in all ages, and with this new feminism stuff there has been a demand for more strong women characters. Sometimes people make them too strong to be interesting. Sometimes people give them the same traits that made their male characters strong and it just feels off.
In yea olden days, man and women were different creatures with different strengths and people were fine with that. Men had it easy to be tough and stuff, women had it easy to be charming and things. And we got good results when a character from one of those camps showed they had made an effort to cross the boundary.
Han Solo - tough guy, sometimes charming. Not very diplomatic.
Princess Leia - Diplomatic girl, charming, brave. Can fight a little, but she's not a brawler.
Now they want these guys and girls to be everything. I'm a girl, and tough, and really charming, and good. I'm a guy and tough, and charming, and good. It doesn't work, it's not realistic enough to be believable.
They're afraid I think, that if they make a character have weaknesses in this political climate that they'll get eaten. That if they make a female character who can't fight, or a black character who is sneaky, that they'll get ruined by mobs of mobbieness.
Anyway, I think Rey has a bit of a character decision ahead; they downplayed her flaws for whatever reason, and if they want her to grow in an interesting way she's going to need some personal flaws to overcome.
Flaws make conflict, conflict drives the plot. Having few flaws doesn't make a Sue, but it does make a flat character.
Luke - Idealism, inexperience, lack of faith.
Ben - Age.
Han - Boorishness, rashness, past mistakes.
Leia - Not a fighter, emotional distress, responsibility to the cause.
R2-D2, C-3PO - Droids, with all that entails.
Vader - Son issues, bad guy.
Kylo Ren - Daddy issues, too psychically and physically strong to be safe with his emotional volatility.
Poe Dameron - Not sure. He might be bad in personal combat.
Finn - Traitorous, friends left behind, not to be trusted but he doesn't interact enough with people who know he was stomtrooper to make it matter. Not too good at combat.
Rey - Initially pretty weak in combat, but they undermine it with her action scenes sooooo....
Captain Phasma - Coward.
FN-2199 - Brave, honor-bound, betrayed by close associate, forgets to watch his surroundings.