As of now, the Melee Attack Bonus is halved for two weapon melee attacks. I am of the opinion that this makes Two -weapon melee attacks somewhat underpowered.

The damage of Melee weapon attacks are proportional to the difference between your attack the enemy's defence. Barring situations where you manage to reach the maximum damage cap (Not that rare but we'll just see how the numbers work out first)..

Dmg = k (Attack - Defence)

(I'll be using the average values for 3d6 (10.5) for the calculations, k is a constant representing damage step)

Attack = Attack bonus + 10.5, using average number

Defence = Defence bonus + 10.5

For One weapon

Dmg = k (MA + 10.5 - MD -10.5)= k (MA-MD)

For Two Weapons

Dmg = k (MA + 21 - 2MD -21) = k (MA-2MD)

The Dmg is lower.

For cases where there is only a passive melee def

One weapon:

Dmg = k (MA+10.5-MD)

Two Weapon:

Dmg = k (MA+21-2MD)

The difference in dmg is k(10.5-MD), and 10.5-MD is negative except for chickenwalkers.

I'm not too sure but the numbers don't look too good.

Proposal: Increase multiplier to 3/4 or 2/3.

The formulas would then be (for 3/4)

Dmg = k (MA + 21 - 2MD -21) = k (1.5MA-2MD)

and

Dmg = k (1.5MA+21-2MD)

This gives a damage difference of k(0.5MA-MD) and k(0.5MA+10.5-2MD), which may at least be situationally positive.

While I do conceed that a two weapon melee attack raises the max damage ceiling using the original formula, in almost all cases, damage would decrease. Combine this with the fact that a single weapon is easier to enhance with MP, and I see a distinct need to improve two weapon melee.