One question no Rey-bashing "Mary Sue parrot" can ever answer
Let's just pretend that we know Rey's backstory, and ASSUME she has never had any experience with The Force before this movie (despite the fact that there are major allusions in TFA to her having experience with it in her childhood, I mean the movie shows her having blocked memories right there).
So we look at three generations of Star Wars main characters: Anakin, Luke, and Rey.
Anakin began training at 9 years old, which was still supposedly too late. Ten years later, he is a powerful Jedi, BUT STILL TRAINING.
Luke's "Jedi development" was absolutely miraculous compared to Anakin, as Luke had negligible training that started at 18 years old. Kenobi "trained" him for literally minutes, and then three years later, Luke trained with Yoda (only concentration techniques, Force lifting and exercise) for AT MOST two to three days. DESPITE no one being around to practice lightsaber sparring with, AND receiving zero lightsaber fight training from Ben or Yoda, Luke was able to defeat Vader in their second fight... and Vader had THIRTY YEARS of training and lightsaber experience on Luke, at minimum.
Also, Vader hadn't been shot in the gut by a powerful weapon and hadn't been cut in the shoulder by someone else before his fight with Luke, unlike Kylo in his fight with Rey. This has to be pointed out yet again because you bashers LOVE to strip away all context... I guess I should also toss in that Kylo is simply NOT Darth Vader and he knows he's not as powerful. So, Kylo was kept at bay by THREE people: Chewbacca, Finn, and then Rey... NOT just Rey alone. I also have to point out, yet again, that Kylo was also offering to train Rey and was not trying to defeat her. I'm also still trying to find the criticism of Finn for being able to hold his own against Kylo for even a few minutes AND being able to get in a hit, even though Kylo was in fact trying to defeat Finn, and Finn has no Force sensitivity that we know of. Problem is, I don't see it anywhere, the bashers just focus on Rey.
Let's also not forget that Luke didn't NEED to fight Vader one-on-one at any point before Empire Strikes Back... Although Vader could already sense Luke's power in the Death Star trench years beforehand.
So here's the question: Given this jump in development speed from Anakin's generation to the next, why should Rey be RESTRICTED (in your argument) from her development being potentially faster than Luke's? Why is it REQUIRED for her to develop slower than or exactly equally to Luke? Again, this question is assuming she is actually developing faster than Luke, which we don't know yet.
Where does your anger over Rey really come from? Once you understand this and admit to yourself why you doggedly pursue and criticize Rey with a term that specifies her gender ("Mary Sue") you may even begin to admit to yourself why this has become such a crusade for you.
But I don't expect any of you bashers to admit it here.