My suggestion is for the creation and addition of one or more spells that lower a target's healing %. This stems from running across healing mobs that either heal-nuke themselves to full, or that come en mass and all of them just spam heal the wounded individual. While a solid DPS character or an insta-kill caster may be able to mop the floor with such mobs with ease, not all characters are built like that.

Suggested mechanics would be targeting a single individual at short-to-mid range. If they fail a Fortitude save, their healing modifier is reduced by 50% for something such as 30 seconds or so. Heal does not remove it, but spells such as Remove Curse and Break Enchantment do. Perhaps a lower level version has a touch range, and a higher level allows an AOE effect. Another suggestion might be to include a small Fort penalty to the target, even on a successful save (so repeated attempts get a slightly better shot at landing).

As for whether it is divine, arcane, or both, or what particular school it is, I leave that up to the devs.

Further supporting this could be the addition of new rune stones that can be added to Cannith crafting. Something like Corrupting Runes or whatnot, enabling non-casters to have something up their sleeve if they're not UMD focused. They could use Evil essences to make.