The general definition of Gary/Mary Sue is a character written by someone into someone else’s already established story, who then proceeds to become a manifestation of the author by being better than everyone else- even if they have had years of experience and the new character none. They have no flaws and end up saving the day with little help. The prime example for this is a new Star Trek Ensign who is smarter than Spock and a more efficient leader than Kirk.

Let’s take a look at Rey. Don’t have much a problem with TFA. But by TLJ, we learn Luke has lost all his optimism for the Jedi. Whhaaa? That was Luke’s primary character trait. It made him stand out beyond even legends like Yoda and Obi-Wan. It’s interesting perhaps for a novel focusing on Luke, but within a two hour movie that’s a lot to cram in. So they spent their time with Luke and turned Rey into the mentor character. Rey is at a point in this film more optimistic than Luke, and later it’s shown she can shoot on the Falcon far better than Han ever did. And to top things off, she lifts all the boulders with no effort, about as much as the x-wing from empire only Yoda struggled so she must have greater will than him too.

To summarize, she’s more optimistic than Luke, a better shot than Han, and stronger willed than Yoda. By the end of movie Rey’s sole point of weakness was crying a bit with Ben, but that was of empathy. So is Rey’s sole weakness that she cares about others? Really?

Rey being a Mary Sue definitely wasn’t intentional; Rian didn’t imagine him being Rey and proving to everyone he was better. It was an oversight, because he was more interested in telling a one-off story with Luke and already crammed with Kylo, Poe, and Finn.