At the start of this strip, Obi-Wan has an overwhelming tactical advantage in the fight at this point in the movie. He should simply win at this point and the fight should be over. After all, he has the high ground. Much higher than Anakin. Surely any lesser advantage that may occur later shouldn't be nearly as decisive.

Transcript

Obi-Wan: You've failed, Anakin.
Obi-Wan: Even if you kill me, Yoda will reveal your treachery.
Anakin: And who cares what an outlawed Jedi traitor says?
[SFX]: Whooom!
{The tower they are on floats towards a lava-fall}
[SFX]: Rooar!
Obi-Wan: You claim to care about people, but you've already destroyed the Order you swore to serve, murdered the woman you loved, and now you're trying to kill your only friend.
Obi-Wan: Can you not see where this ends? Your feelings are a lie!
Anakin: My feelings are the only thing I trust any more!
Anakin: Padmé taught me that. Through her I found humility.
{flashback to Anakin proposing to Padmé}
Anakin: Padmé, we've been through a lot together, and I haven't treated you as well as you deserve.
Anakin: I've been selfish. I've tried to keep you safe, but... it's so hard.
{end flashback}
{Obi-Wan and Anakin jump on to bits of debris floating above the lava on force fields}
[SFX]: jump...
[SFX]: swing...
Anakin: I've decided. After I deal with you I'll treat my allies better.
Obi-Wan: You mean you won't kill any of them?
Anakin: What possible circumstance would ever prompt me to do that?
Obi-Wan: Insubordination?