I have the feeling I will generaly do more damage when dual wielding than when using 2hand weapons but I'd like to know if I understands the mechanics correctly...

Here's how I see it:

1) I use 2 swords with average 20. Assuming I have dualwield at 100% and second attack don't lauch, I should do around 40 dam?

2) Same scenario with a spear with 30 dam, I should do only around 30?

3) If dualwielding usually does more damage, am I right to suppose players (except felar) will usually use spear/staff because the inability of their opponment to parry this specific type weapon? Maybe also because those weapons may reduce damage because of the parry and evade bonus?

4) Last question would be about 2hand swords. I don't see any advantage to use them (assuming my foe also use swords) unless it does more damage than the amount I would do while dualwielding 2 swords (ex 2hand sword with 30 dam vs dualwielding 2 swords with 10 dam)... am I missing something about 2hand swords mechanics?

Thank you for your answers.