As someone who is well in to both sports/competitive and classical swordsmanship I'm perfectly willing to say using only a single lightsaber is far superior to dual wielding. There is very rarely a good reason to dual wield two blades of the same length. When compared to the double sided staff though, that's a difficult question to answer. Personally, i'd probably never use either 'styles'. Single bladed saber with a custom grip (to be more practical) would be the best way to go.
Both double bladed and dual wielding are impractical and, honestly, very likely to get you killed against a trained martial swordsman. That said, the way they use lightsabers since the prequels come out is unrealistic and crazy enough that I guess it doesn't even really matter, lightsaber techniques are mostly rule-of-cool at this point. I always chop it up as useful because of a Jedis ability to see a second in the the future, because otherwise they are all more stage performers than anything else.
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.