Eh, it puts a button on Vader being freshly enraged about Obi-Wan to explain why he loses that focus on him.
Also, I could see it functioning in movie economy to let the audience know that Vader didn’t die on that planet after the duel. And it lets us have some symmetry to see his castle once and then see it again.
It’s far from needed, just musing on it at this point.
That’s understandable. I guess I was subscribing to the Jaws theory, which is “the shark is dead, time to wrap it up”. The last scene between Vader and Kenobi is a powerful one, and that last image of Vader, broken and alone, is great. So to me, that wraps up Vader and Kenobi until the next movie. Time to wrap up the loose ends and finish the rest of the story threads.