The Legends continuity gave every major historical significance of the galaxy to Luke Skywalker. I don't think there were any major failures for the character post-Return of the Jedi. That is why it felt refreshing for him to fail at re-establishing the Jedi Order and losing his nephew to the dark side. He was a hero that couldn't live up to his hero status. Now go ahead and complain about Rey being perfect even though she is at the start of her monomyth. When people try to call Luke a Gary Stu it really makes me reflect on what I've learned from Legends. He kind of was though it may not have been on intention.
This is why I am so hoping that the newly established canon doesn't repeat the same shit only substituting Luke for Rey. I want to see Rey have success when it's time for the audience to say good-bye to the character in films, but not turn her into a true Mary Sue especially when the new EU has attempted to downplay that notion. There are explanations as to why she was good at flying for example. The truth is that nether Luke or Rey are perfect characters, but it just feels that way for different reasons.
The expanded universe is that because it expands upon the main saga which is primarily a Skywalker ordeal. It should focus on many characters defining the galaxy and not just on a single protagonist from the movies that follow their own stories. Rey shouldn't bring back the Jedi Order. She has no reason to after learning about why they needed to end from Luke. If she does establish a new order it should be to show force sensitive individuals what they can use their abilities and gifts for regardless of light or dark. I can see Rey and Ben doing this together where the dark side learners practice restraint. This still wouldn't be the Jedi Order since they wouldn't follow their doctrine and would make perfect sense.
Fans want to claim Rey is a Mary Sue then they should hold off until the expanded universe authors take hold of her and hopefully that would never happen. Give her some historical relevance post-Episode IX and leave it at that. Design and craft your own characters to shape this newly established canon.