In case some of you don't know about this,
If I were to use Pistol/Pistol , and Sword/Pistol , you don't need 3 pistols, just leave the sword by itself, as you swap weapons, your main hand will switch to sword, and your offhand will be the same off hand pistol from your Pistol/Pistol, this applies to daggers as well.
Of course, if you want different sigil abilities, then you may consider getting the extra piece of gear, I think its kind of a pricey choice though for lv80 exotics.
Hope this saves someone~!!