So you somehow imagine that comparing a job trait effect (dual weild) on DPS to the DPS of a weapon unenhanced by a job trait is some sort of valid arguement? Thats about the stupidest thing I've heard and I read Killing Ifrit.
Yes it is a valid form of argument, since it is commonly used! Warrior subs ninja and gets dual wield, ninja has it as a main trait, monk comes with martial arts traits to speed up their attacks. If having ninja main or sub wasn't such a common occurance, then it wouldn't be a valid argument.