Originally Posted by
Sacred Knight
The point of the saga was very much not that Luke had moved past the risk of dark side temptation by the end. That was not his journey in that saga. That's no one's journey because via the mythos that is outright impossible. The point of the saga, as it became when all was said and done, was that the son was the new hope to save the father and they together saved the galaxy. Nowhere in there is the inclination that Luke becomes this figure who could not ever be touched by the dark again. Again the exact opposite is hammered home in not only that trilogy, but the prequel trilogy that followed. That you always, no matter what, MUST be on your guard, because the threat never goes away.
Any argument that Luke should have grown beyond a general threat in his elder years does now and always will lie in a direct contradiction of a piece of Star Wars lore. It can happen again. Johnson didn't HAVE to choose to have it happen again. At the end of the day you could have gone tons of different directions. But he was within the rightful realm of the lore to create such a scenario regardless.