I think it's more broken than that. Attach rating augments correctly that for sure damages are another matter.
And it doesn't explain why I do more damages (significantly more) with a longsword (with my low strength and lower characteristic than my daggers) than with a dagger while dual wielding.
The advantage of daggers are: Speed, critical chance and armour penetration. Dual wielding is a very poor choice for fighters, but an excellent one for rogues.
Dex does work. But for daggers you only get 85% of 50%, or 0.425 per dex attribute point spent. Then comes the dual wielding penalty.
This may sound weak, but remember you pour almost all your attribute points into dex: you need 20 in str and 26 in cunning, the rest goes into dex. This means you get physical resistance, defense, attack and dmg increases for every point spent.
Your above comments prompted me to do a proper dual wielding rogue play through (and not the cunning focused build I did first), specialized as duelist/assasin, it is a ridiculously overpowered build.
With a build topped out at 90 dex, you get 160 defense (never gets hit), 135 attack (always hits), 35-45 dmg, 50-80 crits/backstabs and three times the attack freqency of a sword+board fighter. Talents that turns every hit into a critical hit on a stunned character, combined with dirty fighting and paralyze runes on the off hand blade -> pain.
Cheers