First off, I can’t help but imagine the whole “Rey is a Mary Sue” thing as the purview of some basement-dwelling 23-year old with a bad YouTube channel. Ugh. The whole idea of a Mary Sue involves the existence of a female character who is apparently lacking any flaws or who comes into her abilities without struggle or sacrifice. Some folks seem to think this applies to Rey, which is ludicrous
Yep, Rey shows some pretty quick aptitude with the Force. She’s unaware that she’s Force sensitive, but when she finds out she is, well...she does things. Which is fine.
I’m not sure where in Star Wars it was established that Force-sensitive people have to spend years and years in a Jedi temple somewhere before they can learn to use some Force powers. Luke had never even HEARD of the Force until Ben told him. A few hours later? He’s doing cool things. A day or so later, he pulls on the Force to communicate with a now-dead Kenobi and guide his missile to blow up the Death Star. Sweet.
In ESB, prior to visiting Yoda, Luke is able to yank his lightsaber out of some frozen ice and free himself from being dinner. Nobody freaked out.
Anakin is much the same. As a 10-year old kid he’s already pulling on the Force in able to do things. Hell, he uses “Jedi reflexes” to pod-race. But he’s had no training. Not a single day at Space Hogwarts. None. Did anyone tramp to the Internets in 1999 to cry foul at this? Nope. I mean, they complained about a LOT of other things, but folks being able to exhibit some Force abilities without formal training wasn’t one of them. Ever.
Rey, however, isn’t given a pass. Bogus.
Now, you’ll have folks say that Luke is different because he’s the “chosen one” or the son of Vader and all that. But the whole “chosen one” thing didn’t exist until E1, and Luke being Vader’s son shouldn’t really matter. And really, nobody leveled this type of criticism against Luke. Ever. In the Star Wars galaxy, some folks are born with the ability to do cool things. And these films don’t focus on humdrum B- Force users. They focus on the truly special. Rey just happens to be one of them. That’s why the camera is pointing at her.
Now let’s look at Rey. She’s grown up a scavenger on a planet we can assume is pretty well off the beaten track. Unlike Luke, however, she’s heard of the Force (and, as it turns out, Luke Skywalker). So, she’s undoubtedly heard some stories about the Jedi and some of the things they could do. When she finds out a bit later that she might be able to do some of these things, she gives it a shot, and to her great surprise, she pulls it off. Still, she does nothing all that crazy. It’s entry-level stuff. And again, where in Star Wars is it suggested that Force-sensitive people can’t do this sort of thing? The movies actually suggest the opposite. It’s also sort of hinted at in Star Wars that folks that are unaware of their Force abilities might have been using them in a latent sense for a long time. Again, Anakin is probably unaware that he’s pulling on the Force during his racing. It’s not too difficult to imagine Rey doing something similar as she’s hopping around inside of a crashed Star Destroyer.
And that's the truth.