greek heroes can kill them with 2 shoots, not inmortal at all
but norse have flaming weapons
60 hp is not inmense. Its hard to kill if you dont micro the heroes.
if you dont want atlanteans mass them, start using cavalry in groups to kill each oracle, oracles die very fast and cost a lot, thats the faster way.
instead of nerfing, people should start finding ways to manage 6 control groups easily.
norse have fountain, greeks have temple that heals, units that heal without other units, has life steal.
if you nerf caladria you destroy atlanteans
people need a buff using group controls, that could be done by knowing what number has a militar group to identify groups easily, and people practice managing group controls.