In mono aether Phase Dragons are almost always better. A phase dragon + pillar instead of 2 immortals usually lowers QI and does more damage against a fire shield. In a rainbow no one would use immortals when they have phase spiders, dimensional shields, silences, mindgates, quints, and lobotomizers to fill aether's space. Immortals are only really useful if you know you will face a gravity shield, but you can almost never count on that. Many people have suggested a lower cost or increased stats. Perhaps a poll could be made?