Update: Lowered some values - they made sense when compared to each other but not when compared to the other traits
If we wanna go with x/level I was thinking the following numbers...
Defense: 2
Attack: 1
Magic: 1
Speed: 1 (if you add that trait)
Crit: Static 10% (it scales already) - this still probably sucks because crits are so small, but 10% at least
sounds sexy. Point out that spells cannot crit in the description though.
Elemental/physical resistances: Static 15% (ditto)
Health/mana: 3
Now some comments. I think I will start with health because that's probably the most eyecatching. Most people seem to think +15% is OP, yet I imagine some might think zomg 3/level sucks. Anyway if we look at level 15, where it'll grant +45 HP. If you have 300 HP at that point - which incidentally is what you'll have with 30 con, a reasonable score for nightmare at that level - it's a 15% bonus. Just one that doesn't stay 15% if you should happen to have 40-50 con on all your characters at this point. Not looking at any player in particular.
As for mana I'm really leaving that to you guys, I'm not gonna spend a trait point on that anyway. Feel free to make it +75/level to change my mind though.
Now attack vs. magic. I find it easier to raise magic than attack (not counting buffs though), so in that sense the attack trait is more powerful. But magic is also defense against spells, so it has more than one use.
Speed... at the expense of the dual wield trait. I think 1 might be too little and 2 might be too much, but I haven't seen this game handle fractions well. Seems to me decimals are ignored, not rounded. For example 25 fame = 12% discount, even though 12.5 should be rounded to 13. I believe I have seen some cases of x.9999999999 (exaggerated

) being rounded to x and not x+1 too. Speed is a tricky one because warriors probably have less speed at level 15 than at level 1, whereas mages keep ramping theirs up.
If you wanna keep the dual wield trait, best design combat so that dual wield is a little worse without the trait and a little better with it. I still think it's a Chalassa trap though (or drunken mage player trap). It's risky keeping it since mistakes can only be fixed by reloading/restarting, and especially if you take it just as you pick Chalassa up you won't even notice "hey, her numbers didn't increase".
And lastly defense, I chose 2 because defense numbers are typically higher than attack/magic.
I hope I don't have to explain why the % traits are static
