those people are assuming. . a god is just a person with powers. humans have surpassed gods in power. vulcan has affected people, magic, mutates, machines and cosmic powers with his powers. The brain uses tiny amounts of energy. That is nothing for Vulcan to control or manipulate or shut down. Vulcan had energy manipulation powers BEFORE he fused with Darwin. So losing Darwin would not affect his energy manipulation. Vulcan has not been retconned so his powers have not been altered.