Just had another thought. Since all shields do right now is give you a little extra armour and add 1 AP to your attacks, the simplest "fix", is just to remove the 1 AP cost from all shields.
This means that one-handed simply means you can (and should) use a shield (for a little bit of bonus armour and probably some kind of bonus stat for special shields).
Maybe Larian tried this and thought it was too unbalanced, but I feel like the only viable way to play one-handed right now is simply to unequip your shield.
Are any stat bonuses a shield gives really going to be worth 1 AP on every attack you make?