One handed weapons need a slight increase in damage so that Duel wield is more viable, or alteration to make the offhand calculate off strength, not dex.
At lower levels dw is roughly even to two hand weapons, however as the levels increase there grows a disparity between the two builds in terms of their melee damage output.
One suggestion to fix this is to add more weapon enchantments or variations of things like poisons, and cause them to be only applied to one hand weapons, or scale better with them. This being said, I am slightly ignorant of the DnD Calculations and will need to look more into this. From the early access level it seems to be that most of the itemization here really seems to be for two handed weapons, as opposed to duel wield so it may just be that because of the lack of items you can access, dw is inferior especially with scaling.
Either way, we can really use a conversation about this topic, especially from those who have the knowledge of the math to demonstrate the issues at hand.