it is indeed pretty big.
Average Damage = [Average Weapon Damage] x [Skill %] x [Main Stat Multiplier] x [Additive Damage Multiplier] x [Multiplicative Damage Sources] x [Enemy Damage Reduction]
as the general damage formula shows that increased weapon damage can go a preeetty long way.
id still argue that heir is a lot better, especially due to the free crit chance and lucky hit chance which is pretty big.