perhaps their abilities and kits scale based on surrounding enemies, and that bonus is like, times 5 if that enemy is a champion
so for instance, perhaps a blast that "channels the life force of nearby allies", i.e, a small aoe blast that increase based on how many allies are nearby
and also, maybe a passive that grants buffs for how many allies are nearby, as well as a different buff for how many enemies there are, like, more attack damage and speed per ally, and more movement speed and armour/magic res. per enemy
Then we could also make an ability heals an ally, based on the enemies in a radius around the caster, causing damage to any enemy within that radius, and then that damage being converted by a percentage to heal the ally
i should make a post of this sort of champion...