Right. I've got little experience with swing stuff around (aside from wacking kids with lightsabers when I was little) but I agree with what you've said. But you've got to remember several things:
1. Lightsaber blades don't weigh ANYTHING. So that's gonna make a difference
2. Anyone that does use dual or double-weild in Star Wars would have practiced with it a LOT
3. Star Wars isn't the real world. It's fake. With that in mind, it is canon that double or dual weilders can match with a single saber duelist in Star Wars.
1. That's really another call in favor of single weapons though. You have -far- more blade control with one sword in regards to double wielding. If anything, Luke had the right idea in the EU when his offhand saber was shorter, more like a sort of parrying dagger.
2. Anybody with a single saber would of practiced to the same extent.
3. I think I made that point in my own post, Star Wars is kind of rule of cool. If you watch the original trilogy though, in the few lightsaber battles they had it was very clear the actors had been taught good footwork and movement, it was a lot more believable than backflips.
As it is, the only thing that would stop a real martial swordsman from beating a jedi is their ability to see the future and react to things just before they happen. If HK is to be believed from KOTOR II, you can counteract that by having conflicting emotions and thoughts. Cognitive Dissonance somehow disrupts their abilities.
Anybody remember blaster jedis? What happened to those?