I'd see a decent Hex spell being something that negatively affects all foes* within a certain fairly large area, but the effect on those creatures is minor - -1 to hit, maybe, or -1 to any and all damage dealt regardless of how it was caused.
Come to think of it, ideally this damage-reduction idea would also affect spells cast by affected creatures - which makes it something new; I can't think of any other effect that causes a blanket reduction on all damage whether from spell or weapon. Bane only affects melee, I think.
* - though my preference would be it gets everyone in the area, friend or foe, forcing the caster to be careful with targeting the area and discouraging it from just being dropped onto an existing melee.