It's like that in classic. I'm guessing ever since larian introduced dual-wielding they're scared it'll make backstabber op if they revert it back to % based damage.
Dual wielding is already too strong. At level 5, I'm already critting for around 60-70 damage with a Backstab.
I'd say dual wand is too strong too if it wasn't for the fact that wands are terrible in the first place. Equip a Poison wand in main hand and Fire wand in off hand and enjoy the ridiculous Poison + Fire combo coming out of them.
