Its against Zero-K's design policy to have damage modifiers. Armor is the only exception right now as far as I'm aware. (I'm talking about pop-up buildings and units, and Crabe's armor bonus when immobile)
Instead the devs implement such advantages via physical mechanics.
One might argue Scythes already have an advantage against factories: their weapon is very powerful in exchange for being a melee weapon. mobile units can run away and thus are harder for Scythe to kill (although they're faster than most things). Factories are immobile and as such easy prey for melee weapons.
(I think strictly speaking dedicated AA weapons also have a modifier to prevent them from hurting ground units too much if they hit them by accident or via splash. Otherwise Artemis would be a doomsday device)
