Well the way I look at it, if DEX was an archers primary damage stat, it might be a little overpowered. They would almost never miss combos (one of the biggest TP drains), build TP faster from hitting more often, and their Raging Strike buff would be up more consistently giving the the ATK boost. Then they would get extra damage from DEX as a bonus. Also to address your concern with PIE. I think ARC as it stands is a semi-debuff class. They have Blind, Heavy, Bleed DoT, and Bind. PIE could play a pretty heavy role for ARC regardless of damage. A lot of current moogle strategies involve Binding as an example.