I was curious about Vlad’s interpretation of if Obi-Wan (and by extension Yoda) were wanting or expecting Luke to kill Vader, so I tried to see if I could find Lucas saying anything about it. I did manage to find this quote from Lucas in the Making of Return of the Jedi book.
“The mission isn’t for Luke to go out and kill his father and get rid of him. The issue is, if he confronts his father again, he may, in defending himself, have to kill him, because his father will try to kill him. This is the state of affairs that Yoda should refer to.”
I think that lines up with what Vladius is saying.
I don’t think that Luke’s mission in ROTJ was explicitly to kill Vader and Palpatine, only that Luke should be prepared to do so should the need arise. Luke himself points this out and Obi-wan confirms it.
ROTS on the other hand is explicitly an assassination mission for Yoda and Obi-wan, one which Obi-wan believes he has completed by the end of the film.
I think that is where the confusion comes in. Some people say that Jedi aren’t killers or assassins and point to one trilogy to confirm it, while others say that the Jedi can absolutely be assassins and point to another trilogy to confirm it. Kenobi falls directly between the two trilogies and so there’s no stable baseline for Jedi behavior to fall back on, and so people have to justify Obi-wan not completing the explicit orders of his master by saying that it’s not the Jedi way to kill a guy in a lightsaber duel who has forced you into a pit and who’s now standing there astonished by the power of your second wind.
Vader even retains his saber at the end of the fight, so the comparison to Maul is almost one to one.