Oh don’t get me wrong, I also feel like just having Obi-Wan walk away is a weird choice that I don’t agree with. Especially when Obi-Wan, earlier in the same episode, said, “It ends today.”
Just to have him walk away again, it basically puts us back at the end of ROTS, except Obi-Wan is less guilty now I guess.
And that alternative isn’t bad, but you still end up with Obi-Wan leaving Vader for dead, and not actually making sure he is dead.