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.
This was ultimately the reason (and Reeva nonsense) that I decided to completely cut episode 6. Repurposing the duel for the bacta tank does something we haven’t seen in star wars yet. The cave on Dagobah teased it, but now we have a completely internal battle with Obi-Wan. The moment he apologizes to Anakin, the truth comes out, and he is released of the guilt and regains his strength. THAT in my opinion is a compelling and new narrative.