Regarding the jedi masters’ intentions in ROTJ, I had never given it much thought to be honest. I don’t think I even realised there was a debate until recently. To me it was clear that both Obi-Wan and Yoda wanted Luke to kill Vader, for several reasons:
Obi-Wan says that they have already lost when Luke says he can’t kill his own father. He then shuts down the idea of redemption when Luke suggests there is still good in Vader. This would be some really bizarre reverse psychology if Obi-Wan actually intended for Luke to somehow stop Vader peacefully. Also, this is not totally solid as it was cut, but in the ROTJ script there is more dialogue in this scene and Obi-Wan says quite explicitly that Luke is to ‘destroy’ Vader.
Yoda’s intentions are less clear in dialogue but I still get the impression that he wanted Vader to be killed. He says it was ‘unfortunate’ for Luke to find out Vader was his father, and considers the knowledge a burden. This could really only be the case if the intention was for Luke to kill Vader. If the plan was for Luke to somehow turn his father instead, knowing about him in advance would have been more of an asset than a hindrance.
Lastly, the dramatic tension of the film hinges on Luke believing in Vader’s redemption when literally no-one else would. He manages to force a resolution without resorting to killing, defying all expectations in the process. It’s bizarre to me to think his mentors secretly wanted the same thing, and they just refused to say that or worse heavily imply the opposite.
Regarding the outcome of the duel in OWK, it looks dumb to me. The whole exchange is quite nice but walking away seems contradictory. If Obi-Wan finds some peace in knowing that Anakin is gone, and that Vader killed him, shouldn’t he find it easier to finish the job and kill the enemy? There is no conceivable way that leaving Vader alive would benefit anybody. I never really liked the resolution of their fight in ROTS, and how Obi-Wan just let his old friend burn instead of putting him out of his misery; but at least then he had reason to assume he would die from those injuries. Obviously the real reason in both cases is that Vader had to survive for later films, however they could have been staged differently to make Obi-Wan’s decisions look less questionable.