^This!

there are many little things that could have been used from OT to make the PT more "canon" ...

Anyway, I had some thoughts when reading about the final of Rebels and possible connections to Clone Wars:

- it would have been cool, to see two or even three "Sith" battle against each other (like was done in the Clone Wars), giving this idea more weight:

-- we have the character of "Maul", who acts as "General" for Sidious/Dooku, in Episode 1 he is wounded, but not killed, in E2 he is then presumed dead, only to reappear in E3 as "Grievous" (or "Vader")

in parallel to this, Anakin has similar trials, and loses arm/legs along the way to the final confrontation - ending with his duel against "Maul" (aka "Grievous")

So where does that leave Obi-Wan? maybe he didn't duel him then (resulting the lava beach and later breath-suit), maybe OB1 just faced "Vader" and held him off, to help someone (Padme or Bail Organa) escape to safety (or hiding) ...