Okay I have been running some tests.
Xsabor: 13 damage water weapon if anyone forgot

The numbers within parentheses are the damage distribution of the actual attack (mainhand+offhand). On a curious side note, yes I do notice that all my attacks did max damage.
NO TRAIT
Ranger attack: 47-48
Target defense: 37-40
Target water resistance: 0-5
2x 15 DW: 24 (19+5)
Xsabor + 15 DW: 27-30 (25+5)
15 + Xsabor DW: 23-26 (19+7)
----------------------
WITH TRAIT
Ranger attack: 48-49
Target defense: 41-43 (I gained a level, so the target did too)
Target water resistance: 0-5
2x 15 DW: 33-36 (19+17)
Xsabor + 15 DW: 41-42 (25+17)
15 + Xsabor DW: 40-42 (19+23)
Firstly I'd like to say the traitless numbers look correct. Offhand damage seems to be penalized down to 25% indeed, with some slight tolerance for whatever rounding is happening behind the scenes, plus of course the damage range. But with the trait, no. Look at the 15 damage weapons: 19 in the mainhand, 17 in the offhand. Now look at Xsabor: 25 in mainhand, 23 in offhand. What's 90% of 19? What's 90% of 25? I think the trait doesn't make your offhand deal 65% damage instead of 25%, I think it makes it deal 65%
extra damage, so 90%. You can also try dividing their offhand damage without the trait by 25 and multiplying it by 90 and then compare it to the trait-offhand-damage to see more "data" to suggest this.
If this is the issue, I still think fabulaparva's numbers will be pretty damn impressive after the fix. When I said 65% offhand damage for the trait, I was assuming that after "calculating" the raw damage - the weapon damage of a twohander, or the mainhand damage plus the penalized offhand damage - the other mechanics would treat them equally, but there seems to be something in the formulas that benefits DW more than 2h. I'll see how DW vs. 2h feels in act 2 when I get there anyway. I don't think the elemental damage calculations are to blame for anything though, and obviously not Cross Cut either: It is dealing double damage, as advertised.
P.S. to fabulaparva - do you actually keep different elemental weapons around in your inventory and switch them from encounter to encounter? It's just a game you nerd!
