Luke is thus essential to the Star Wars universe because he represents the change to the Jedi Order. Luke follows Anakin’s path as a Jedi (strong force potential but “too old,” emotional, etc). However, Luke is not surrounded by allies who force him to keep his emotions shut but friends in Han and Leia who allow him to mature and grow as a person. He isn’t just told the dogmatic ways of the Jedi order and thus is able to form his own opinions and beliefs, the most important being just because a person has fallen to the dark side doesn’t mean they are irredeemable.
the final encounter with Vader and Palpatine is thus the culmination of this belief. Yes, Luke does strike first and Palpatine senses his anger and emotions. Yup, Luke does give in to anger, powering his strikes to then overpower and disarm Vader. However, the key point is Luke choses to not be a Sith, reaffirms that he is a Jedi despite his emotions, and like his father before him you can have emotions like anger and still fight for good.
Luke is rewarded with this by the fact that Vader chooses of his own will to kill the emperor, sacrificing himself in the process. The most powerful scene is arguably after the fight, where Vader asks Luke to take off his helmet and reaffirms that Luke was right about him, that he was right that a Jedi doesn’t need to be emotionless and that even a Sith Lord like Vader can return to the light.
the fundamental problem with the ST Luke is this how Luke seems to throw his message away. One of the most exciting aspects of the potential ST imo would be the reveal of Luke’s new Jedi order. This has been explored in the EU, allowing Jedi to form relationships, marry, be actual humans. This is due to the fact that Luke understands that emotions like anger are natural to living beings and just because you express those does not mean you fall and become a Sith, nor does it mean you become irredeemable.
However, TLJ Luke reverts to PT Jedi beliefs, believing if a person is fated to fall to darkness, he is irredeemable and thus must be killed. Honestly, if it were not Luke but Obi Wan or Yoda training Ben, the TLJ actions make sense. These Jedi firmly believe once a Sith always a Sith and thus it would be justified to kill him before he comes to power.
However, Luke is different. He recognized the flaws of the previous Jedi Order and was even reaffirmed this by his father, the one who he redeemed. ST Luke doesn’t make sense to me because his story trajectory and the lessons learned from his journey are contradictory to his actions in TLJ.
Luke shouldn’t have tried to attack Ben, even after the vision. Maybe break down crying from sadness that his family may be tainted by the dark side but not attack (like the reveal that his dad was Vader). Luke also wouldn’t have given up on Ben, believing that he could have been redeemed and brought back to the light against all odds. He did for Vader when Obi Wan and Yoda didn’t. So why so different for Ben?