I think it would be intresting if Vader did indeed kill Luke's father

Then Jedi really would have been about Revenge rather than redemption of the father.

It would fit the classic kung fu, judo or samurai stereotype of the student avenging the master, that on top of an adversary who killed the heroes father.

It would also have been about restoring honor to the jedi school by bringing Vader a fallen Jedi who misuses his training to justice.

Lucas instead decided to go with a more traditional mythological idea of the villain being the father, also very Freudian or Jungian, but certainly absorbed by Joseph Campbell.