Does anyone know if there is a dual-wield penalty (absent a feat), like in 5e? Or does costing a bonus action take the place of the penalty?
The penalty is replaced by the fact that offhand damage does not add the Ability modifier (absebt a feat-like choice, e.g. Two Weapon Fighting class choice for warriors).
On the other hand, 5e removed APR and automatic offhand attacks, so attacking with the offhand costs a bonus action.
