This is Carrion Fields, not third edition Dungeons and Dragons. Things work differently here, but no less logically. CF seems to take into account what D&D doesn't: if someone is properly trained in a two weapon combat technique they are just as or even more effective then someone with only one weapon. Fencing with both sword and dagger is a real world example of an attempt at this, though possibly not as effective as Carrion Fields dual wielding.

The Imms haven't weakened dual wielding, therefore they appear to feel it's balanced and shouldn't be changed. As someone else pointed out, there's advantages to dual wielding and advantages to not.

As for two handed weapons, their inherent average damage and dam bonuses appear to already take it into account, as do the skills used with them. If the damage were not set at a level to make a two handed weapon reasonably hard hitting, I'd think the Imms would already have looked into it. Again, this isn't D&D, so the game mechanics can't be expected to be the same. In other words don't expect the character's total +dam to be increased just because they're using a two handed weapon, any appropriate +dam bonuses would be included as part of the weapon.

(disclaimer: I'm fairly sure I understand the mechanics on this issue, but I could be wrong. If I am, I'd appreciate corrections from someone who knows how it works for certain)