I found a way to defeat them last night when I was playing control. Be a titan defender and pop your ward of dawn with armor of light and sit in it. The blade dancer per strike will only take down one quater or half of the shield, by that time the ol' buckshot melee move will take them out. Then simply re-enter the shield to replenish your defences.
English
-
I've been maining Gunslinger and if I find myself against a BD-heavy team, I'll hold onto my supercharge until I hear someone activate BD. One shot kill to prevent a knifing spree and you can feel their rage... Also, I've been having some great fortune in taking them done before they get to me even without the super. Gambler's dagger + knife juggler means I'll typically have at least one knife on CD. Throw one (or both if available) of your knives at an oncoming BD and if you can manage to get off some headshot rounds they'll fall far before they get to you. In close quarters, though...