With that said that’s still not a good reason for Obi Wan not to kill Vader in this moment in the show. For that I just assume he can’t bring himself to do it, which is the same thing he had in Revenge of the Sith. He has pity in the same way Bilbo and Frodo have pity on Gollum.
The problem with that is that, like you said, it’s the same. The context of the duel has to be different from what we saw before in RotS to feel meaningful & additive to the franchise.