Everybody always argues about Rey being too overpowered, or never failing, or definitely failing all the time, etc. Debating whether or not Rey’s “fail count” or “Mary Sue score” approximates Luke’s “fail count” or “Mary Sue score” overlooks the real underlying problem with TLJ’s themes and message.

In terms of Rey’s arc, TLJ presents three inter-related messages/themes:

Failure is a great teacher
Elders from the past can teach us what types of failure to avoid
Apart from learning what failures to avoid, there is little else of value we can learn from elders or knowledge passed down to us, so we must look inward to ourselves to move forward

In isolation, Message (1) and (2) are good messages. However, the way the movie connects Message (1) and (2) with Message (3) is very harmful to Star Wars (and harmful in general).

But since this is controversial, first I’ll provide evidence that TLJ actually conveys these messages. Message (1) is conveyed explicitly through dialogue by Yoda. Message (2) is presented in various ways, such as when Yoda says “Luke, we are what they grow beyond”, and when Yoda tells Luke that the most important thing he must pass on is his follies and failures, so younger generations can grow beyond them. Message (3) is an extension of Message 2, and is presented explicitly when Yoda mocks the “sacred Jedi texts” and says “that library contained nothing that the girl Rey does not already possess”, before literally burning down the library. Message (3) is also presented through Rey’s journey throughout the film, as Rey doesn’t actually learn much about being a Jedi from Luke. Luke mostly teaches Rey how the Jedi failed or were wrong, while Rey trains herself and then takes the ancient texts along with her so she can self-learn. The over-arching message here is that knowledge passed down by elders is only useful so we can learn how to avoid past failures, but in terms of going forward and learning/achieving new things, there is little our elders can teach us, so we must look inward to ourselves.

Now, while these themes are prominent throughout TLJ, the movie also muddles these messages a bit, which can easily be mistaken for intentional nuance. These messages are muddled in four primary ways:

Message 3 is also conveyed by the famous line from Kylo Ren “Let the past die”. But since Kylo is a villain, this dialogue is presumably not meant to be taken as a teachable moment for the audience.
Message 2 and 3 are conveyed by Yoda, but Yoda himself comes from the failed past, so why should we even listen to him?
Yoda says the Jedi texts are mostly useless to Rey, yet Rey takes them with her anyway.
Yoda also mentions two positive things (strength and mastery) as things that should be passed down by elders

I believe these muddled aspects and inconsistencies do not represent any intentional nuance in the overall message. They are mostly just inconsistencies/contradictions in the writing. In regard to Rey taking the Jedi texts with her, this was probably included so Rey had some way of learning more about the Force after Luke dies. With the Jedi texts, Rey can learn by herself - rather than learn from an elder. (The fact that the texts themselves were written by past elders is probably another oversight not to be taken as intentional nuance). And as for “strength and mastery”, despite this brief lip service to past knowledge, Rey does not actually learn any “strength and mastery” from Luke. She learns those things by looking inward to herself.

Regardless of the inconsistencies, the overall message is pretty clear: “knowledge/ideas passed down by elders is useful mostly so we can learn to avoid past failures, but there is little the past can teach us as we move forward, so we must look inward to ourselves.” In my opinion, this is a harmful, insidious message that, when taken to its logical endpoint, results in solipsism and narcissism.

Instead, Star Wars should portray the learning process as a give and take between elder and younger generation, with the elder conveying most of the knowledge, but the younger offering a unique perspective that forces elders to reconsider long-held beliefs. The OT did this perfectly, with Luke learning from Kenobi and Yoda, but also proving them wrong by redeeming Vader.

Finally, it’s true that Rey herself also fails badly in TLJ. This is what the “Mary Sue” crowd doesn’t acknowledge. Rey gets her ass kicked by Snoke, she has to be saved by Kylo, and then she fails to bring Kylo back to the light. Now, Luke definitely fails more often (let’s get real here), but this is actually not even relevant. The important point is that Rey’s strength and power come almost exclusively from looking inward to herself and tapping into her inner strength, not by learning from an elder mentor who bestows knowledge from the past. This is an extension of what happens in TFA, where Rey’s Force powers spontaneously manifest with no prior training. It’s also why Rey sees an endless reflection of herself during her vision in the underground cave. TLJ ends triumphantly with Rey lifting tons of boulders - a feat that nobody taught her to do (apart from some meta-joke about lifting rocks). Rather, it was only her own inner strength that enabled her to do it.

And that’s the real difference between Rey and Luke. Both of them experienced failure. Both had some “Mary Sue” moments. But Luke learned from elder mentors. Rey learned that she only needed herself.