Of course the main reason why the saber fights in the OT were due to a lack of 'inspiration' during the 70s and 80s, that goes without saying.

However, if you go by the story, then it assumes that there are very Jedi left in the galaxy - Luke is proclaimed to be the last of the Jedi by Yoda on his deathbed and Vader is the only Sith, if you believe the 'There can only be two Sith' rule.

You can then assume, although assumptions are the basis of all f**k-ups, that Obi-Wan will have had little use for his lightsaber skills over the 20 years, preferring instead to train himself to be able to pass his spirit on into the Force and hide his presence from Vader. Vader, equally, will have had little use for his lightsaber since a little Force choking will have been enough to settle most 'disputes'. Therefore, going by logical thinking, the skill levels of both Vader and Kenobi will have remained static at best, possibly even dropping due to years of non-use. Even if you factor in Dooku's prancing about in the PT, he does have the added 'bonus' of being an old man in at least active Jedi times, not when there are 3 of them left with 2 of them hiding their presences in the Force.

Anyway, that's all I'll say on this...(I have no idea if it does make sense to anyone other than me! It is an opinion and all opinions should be respected no matter what the subject.)