yes absolutely, thats what I am talking about.
it was argued that luke turning to the dark side at the end of ROTJ would be an absurd twist because it would be against everything the character stood for over three movies. but thats what happened to vader, when it made even less sense with vader, because he never questioned himself. he was the iconic ultimate evil for three movies at the end of ROTJ.
Luke wasn't static in the OT though. He starts as a young, bored teen who wants adventure, becomes a soldier who still carries the impetuous nature of his youth, and eventually learns his lesson about his temper and overcomes his anger problems to defeat the emperor through
love. His internal "dark side" has been
defeated. He proved the old Jedi Order wrong by claiming victory through his love rather than letting his love cause him to give in to his anger. He faced down space Satan, was tempted to the point of almost following, and emerged triumphant. He faced the problem that his father faced - whether to turn to the dark side to save the ones he loved or whether to trust in the Force - and where Anakin fell, Luke succeeded. It was set up that way on purpose in the PT specifically to show Luke's valor.
None of this would matter if he goes and turns to the dark side anyway later on.
What's a little more ridiculous is that the act of saving Luke and killing the Emperor counted as redeeming and saving Vader after all the evil he did, but I guess in the Star Wars universe that's enough to redeem someone. I feel more like it showed the capability for redemption, and a turning point toward it, but the movie counted it as the full thing.
It's a very Christian concept of redemption, which is a little odd in the Star Wars universe which seems to be mostly influenced by Buddhism, but it fits when you think of Vader as a sort of space Jesus as the prequels turned him into.