While this will likely come off as blasphemous the question has only begun to gnaw at me: Aside from being the last and thus only one, what made Luke a great Jedi?
Excluding the extended universe, which actually no longer exist as possible canon, you've got an initiate Jedi who took out the Death Star with basic perception skills, saw Yoda lift and move an X-wing but never did it himself, leave half finished training to lose his hand, look for and rescue Solo after months while refining what he learned, and finally be the key thing that turned his father from the dark side.
Again, just looking at the original 4-6 trilogy, in what way shape or form was Luke one of the most powerful Jedi ever? One who apparently pulled off what no other could by the time the Last Jedi came around?