<<no, we see Rey scavenging parts of wrecked ships, cleaning them up and selling them to Unkar Plutt. What we don't see is Rey as a scavenger getting ships working again>>
We see her fixing starship parts. Starships are made of starship parts. And she has. knowledge of the 'Falcon's maintenance history.
<<but Luke didn't understand R2 right away. 3PO was there at the beginning to translate. Later, in Luke's X-wing, R2's bleeps were translated for Luke on a monitor. Then after that, Luke picks up what R2's saying. Rey understands BB-8 from the get-go. It's ridiculous.>>
Maybe she's worked with BB series droids or other astromech droids? Unlike Anakin, who seemingly only knows standard, Rey might have a talent for languages having been exposed to more in the obviously more comopolitan environment she was in than a farm on Tatooine. Note, rather than saying 'I can talk to my phone and my phone can talk back, why on any given planet can't astromech droids talk standard', you go "ARGH! A girl is talking to a robot". :-D
Your lack of suspension of belief seems a tad gendered.
<<We don’t know her real backstory - admit it, Rey shouldn't be able to understand Chewie. Rey's never been to Kashyyk, and there are no Wookiees on Jakku>>
You know this how, having admitted we don't know her backstory.
<<this is true but throughout the OT Luke learns, makes mistakes, learns from his mistakes and becomes more powerful. The Luke in ANH and the one in RotJ are in two very different places>>
We certainly see Rey gain power as she realises her latent Force powers. By the time she does the rock lifting she has arguably had more training than Luke had when he destroyed the Death Star with an impossible shot.
<<these are some good points, and I wish the new trilogy explored Rey's character and background a bit more. But with Luke the risk-averse background contrasts well with his yearning for adventure. He has 'too much of his father in him.'>>
Well, maybe in a non-creepy way Rey has some of her father in her? Lack of backstory.
<<Being a good shot as a pilot is part of Luke's skillset. He 'used to bullseye wamp rats in [his] T-16 back home, and they're not much bigger than 2 metres.'>>
Yes, an unmounted rifle in a T-16 is EXACTLY like the quad cannon on a X-Wing, Oh, except they are not. Likewise, a torpedo targeting system is utterly unlike a slug-throwing rifle you hold to your shoulder and sight using your eyes.
<<With the Death Star shot, perhaps he got lucky. Or, seeing as Luke had already been introduced to the Force, perhaps he used the Force.>>
It was the Force. There is no suggestion it was luck anywhere in the canon. But good to know that boys can get lucky...
<<It's interesting you said this comment in reply to my point about Rey pulling off a Jedi mind trick just like that, with no training. You have no answer to that>>
Yeah, I missed that. Never seen people dancing and exchanging moves? Naturally skilled dancers can watch someone do something and duplicate it. Hell, Mozart at age 14 heard 'Miserere' a 14 minute long complex choral piece performed in the Sistine Chapel, went home, and wrote it down from memory (thus committing one of the first recorded acts of music piracy as the score was not freely available then). Rey simply reverses the trick that Kylp tried on her. Nothing someone who is not naturally talented could not do in the real world with something they were talented.
<<no, I didn't miss it - that's the whole issue. Rey is very powerful and does amazing shit with no training needed. It's ridiculous. Imagine if Luke had done better Jedi stunts than Yoda that first time on Dagobah, or if Luke had somehow bested Vader on Bespin. That's the level of Mary Sue/Gary Stu and dumbf**kery we're talking about here>>
<<Yeah, Luke had shut himself off from the Force, you are comparing apples to oranges.>>
<<no, I'm complaining that Rey is brilliant at everything, first time ... that there's little opportunity for her to overcome adversity (she just needs to turn up because she always wins), that there's no opportunity whatsoever for her to learn from her mistakes (she doesn't make any), that as a consequence of all this, there's little opportunity for her to grow as a character.>>
In general the pacing of the movies is shit, for all I enjoy them vastly. ANH and TLJ are meant chronologically to be immediately one after the other. They've removed the travel takes time concept, by and large, although bring it back in when convenient, thus destroying a vital narrative conceit; the cavalry is literally always over the next hill now. It is this which leads to the frenetic pace and the lack of story arc. No SJW agenda, just unnecessary story-telling choices. But I bet you've not complained about the lack of scenes of Legolas collecting arrows...
<<Rey is a Mary Sue>>
No Rey reveals the ultimate issue when you have a 'magic' system, by whatever name you call it, that is essentially made up as it goes along. There's old non-canon (now) novels where Luke pulls Star Destroyers out of orbit using the Force. It's the same narrative path in Dune with Paul as the Kwisatz Haderach, the same issue with Hermione Granger and time-turners. You are criticising faults that a premise and poor story development inevitably lead to, regardless of gender, but are getting a tad hysterical about it because it is a girl. Star Wars has shit internal logic, as does Harry Potter. Plot Holes the size of stars. But you're only excited about this one because it is about a girl.
<<In the one moment in TLJ where another character out-Mary Sues Rey, we see Leia fly through space - what in the everlasting f**k?!
Nope, you being too invested in your precious head-canon to accept the twin of the powerful Jedi might have in extremis unexpected abilities. You miss out on the emotion of the scene you're so busy looking for testicles or the logical development of an illogical inconsistent magic power that never has a logical development.
<<As for explaining the SJW propaganda>>
Yup, there we go again. Loaded language. I warned you. And you should know better. Likewise, using ad hominem to attack someone on account of their weight! Really not doing yourself any favours and highlighting that the issue here is not anything to do with Star Wars but everything to do with your attitude towards gender and a shitty attitude towards other people from the safety of a keyboard.
SJW do not exist except as a pejorative term used by those who are unable to come up with a concise description of the behaviour they are criticising or the identity of groups that exclusively engage in those behaviours, or even the listing of a local SJW group.
You can find a local feminist group. But you won't be able to find a local SJW group. You're using loaded language. And anyway, wanting social, racial and sexual equality is not a bad thing. That's what social justice is. You fighting against that?