At any Havoc level, this combo feels absolutely atrocious. The mobs with this combo take far too long to kill, largely due to inability to target the healing mobs within the packs. And since you cant kill the things around the healer, you must resort to looong kiting dances, chipping away at the healers with splash damage and/or lucky melee hits. The challenge spirals out of control if the kiting is forced to progress forwards in the map, grabbing even more mobs and triggering boss spawns.
Proposed change:
Garden mobs start with a set amount of healing. After healing allies for that amount, the effect drops off.
This allows all damage to all mobs to have a cumulative beneficial effect to the team and eliminates the infinite grind potential that a strong pack of armored/healing mobs creates, all without removing the unique challenge presented by the healing effect.