well, can i throw out there that we need a more convincing fight between Kenobi and Vader? Kenobi at the time of ANH was actually younger than FOTJ Luke Skywalker, am i right? He was also more than 20 years older than Count Dooku was when he fought several stirring battles before dying.
Vader should use the force in their combat to gain an edge over a perfectly healthy Kenobi, whose lightsaber skills shouldn't really be all that diminished, since his connection to the force (the driving heart and soul of any lightsaber duelist, and especially kenobi) should have been even stronger than in ROTS after 20 years of studying the force on Tatooine.
I might write a new fight for them. Same result, more realistic struggle.