Since we're talking about Grayface, he made another massive change to dual wileding in MM6 which *almost*
makes up for Armsmaster not being present in the game:
Wielding a sword or dagger in the left hand does NOT remove the damage bonus for using a mace/spear/axe.
It does remove the "attack bonus" you get from said axe/spear skill, (replaces it with Sword's, exclusively)
but that's quite OK, since using 2 weapons already
gives you a big bonus to "attack bonus" anyway from the weapon's own "+" bonus.
In MM7 and MM8 on the other hand, (still talking Grayface) using a spear+sword or axe+sword combo is not effective at all, since the sword/dagger being present removes the damage bonus from the spear/axe skill.
Still, dual swords is effective (no damage bonus to be had), also one sword+one dagger, or two daggers, are all effective combinations (the dagger GM damage bonus is never removed, as long as the dagger is wielded in the left hand).
If you wield a dagger in the right hand and sword in the left hand, the bonus is removed!
Al in all, I'm very pleased with the balance, since MM7/MM8 already have the Armsmaster skill which adds damage on top.
The Grayface patch I'm using is not up to date, though. Maybe he decided to change this formula in later patches...
Let me know if this is the case.