Yeah, you're melee dps (weapons) have no bearing whatever on your special abilities. Neither do Agil or Str (although agility adds to your pwr pool if you're a scout). If you want to back-stab better, upgrade it to app3, adept1, master, or whatever.
I find that I use short-delay dual-wield weapons almost exclusively. There are times that having the extra AC of a shield is handy (when soloing hard stuff)... so in those cases I just throw on any-old onehander and let my abilities and poison do the killing.
But in case you're wondering, it's usually said that dual-wield weapons are the best damage per second you can get.