In terms of damage output, dual-wielding is only useful against targets with low Soak...
...and in some corner cases involving special preparation or very specific character stats.
To see why this is so, it's helpful to ignore the to-hit penalty at first and concentrate on the time issue. Since a two-weapon attack takes 4-m instead of 3, we can say that a two-weapon attack is equivalent to two one-weapon attacks at 75% of normal damage. In other words, a two-weapon strike does 150% damage. But remember that this is damage, not wounds! Both of those attacks are still reduced by the enemy's Soak, so against your 150% damage, the enemy effectively has twice their normal Soak. If their normal Soak is already respectable (say, 7 or more), then this doubling effect can be show-stopping.
In fact, the situation is even worse than that, because there is a third, unstated caveat:
- You can't dual-wield large weapons.
You can two-hand a weapon up to your Size + 2, but with one hand you can only wield a weapon of your Size. As a result, you "lose" two points of damage when going from a two-handed to a one-handed weapon.
Let's run some numbers. Suppose you're well-specced for combat, as a Size(3) character with a choice between one Size(5) or two Size(3) axes. Your damage with the large axe will be 17/20/26/38, while the damage of each small axe, including the 75% factor, will be 11.25/13.5/18/27. If your target has a Soak of 7, equivalent to full-plate with no other bonuses, then your wound output will be 10/13/19/31 with the large axe, and 4.25/6.5/11/20 with each of the two small axes.
So you see that, at the minor and moderate success level, dual-wielding is actually detrimental in this case. At the major level, dual-wielding is slightly better, and then much better at the complete level. The result only gets worse if the enemy has a larger Soak, or if you're not as optimized for doing damage.
The situation becomes even more grim when you bring the to-hit penalty into the picture. The whopping -7 penalty for the off-hand weapon means that your off-hand weapon will probably score one success level lower than your single-weapon strike would. For example, if our Size(3) warrior above consistently scored in the middle of the major success range with one weapon, then dual-wielding would "decompose" this major success into one major and one moderate. Looking back at the numbers, a single-weapon major success would do 19 wounds, while a two-weapon major + moderate would do 17.5. So dual-wielding once again turns out to be worse than single-wielding. This "decomposing" effect only vanishes if your average to-hit roll is 13, 14, 15, 23, 24, 25, or 33 or higher. (In fact, if your average roll is 1, 2, 6, 7, 16, 17, 26, or 27, then both of your two-weapon attacks will be one success level lower on average!)
In summary, dual-wielding is actively harmful to your damage output unless:
- the enemy has very low Soak, or
- the enemy has middling Soak and your average roll falls in a specific range, or
- you are an unstoppable warrior-god who consistently rolls complete successes.
That said, special preparation can make dual-wielding less useless.
Since you do get two attacks instead of one, any damage bonuses and per-attack effects will be magnified when you are dual-wielding. This can be devastating, if you have the time, foresight, Fatigue, and good fortune to activate these effects before you start fighting. Useful effects include combat-related Stunts; the Shadow Power "Negate Armor", which allows a few of your attacks to ignore Soak; the Emotion Power "Allied Attack", which grants +1 damage on each attack per nearby ally; and a few Barrier Abilities from the Body and Physic trees.
