You either have horrendous lag or awful aim, since the Bladedancers I've encountered are nowhere near as immortal. I've killed some mere inches away after sticking them w/ a magnetic grenade and firing some shots, brutally murdered 2 in a row w/ rockets, and simply gunned down others as they were approaching me. Granted, they were mid-distance or greater from me, which may have been bad timing on their end or good timing on mine. Of course, I've met my demise at the hands of Bladedancers countless times, but that was mostly due to my inability to examine my surroundings and use them to my advantage. If you get killed by Bladedancers/Gunslingers so often, it's because you're out in the open for too long. It's where they excel, so use cover to your advantage.