They should apply 'Backstabbing' just to dagger. If you equip a dagger you can backstab with it, otherwise you can't.
Yes. Change the dagger's damage or critical multiplier, or something else, but please, ditch the Backstabber Talent. It was somewhat annoying in D:OS 1, but that game gave you two starting Talents and a third at level 2 or 3. This game gives you one and the next at level 4, making the Talent Tax of Backstabber move from annoying to detrimental.
