This is my understanding; 1h and shield and dual wield have lower damage per weapon, lower enchantment affects, and lower trait effect to make it fair when compared to a single 2 handed weapon which gets larger damage, larger trait effect, and larger enchantment effect.
One thing that 2 handed weapon users lose out in a big way is the loss of a slot for a set piece slot. My thought is the addition of a pommel or trinket slot when using a 2 handed weapon. This slot has no enchantment or trait but only a set piece. I could be wrong here but it seems it would be a fair thing to ask for. Thank you.