I just tested this by making a unit with high Dexterity and sure enough, they get no bonus to crit. There is certainly room for improvement here. There should be and incentive to get a high dexterity to crit better. Axes give +1 to crit, but since it is disabled apparently for regulars, it only works for heroes. Axes are essentially useless.

There is little reason to choose any weapon for a specific goal. If this is a design choice, I would implore you to rethink it. Why ignore a divine opportunity for unit tactics differentiation? I could make archers that have extra Dexterity so that that there might be a reason to pick the +3 Dex trait when designing them. Right now the only good traits are Bloodthirsty and +3 to Accuracy. It might also be noted that Archers really have no need of the current armor options. Some special armor or clothing might be nice to round these units out in the late game. 

The point should be to make the player choose an armor combination and weapon type. Right now we just tech past a whole load of weapons that are never useful again. I would like to see some better differentiation in weapons and armor.