There are now two stats named Weapon Damage, the previously existing one in the Stats & Materials overview and the new one which replaced the former Attack Power, with differing values
The one in the Stats & Materials overview states the combined base attack damage of the equipped weapons. The new one replacing the former Attack Power instead multiplies the Weapon Damage and the Weapon Speed stats from the Stats & Materials overview 
Why do two stats with the same name use two different calculations?