i dont have a problem with immortal, personally. it is a low cost immaterial creature that can provide damage while dim shield is up, and not draining the quanta too much, like phase dragon, to keep the dim shield chain going if you do have have excess pillars.
immortal is strong defensively and as such provides consistent offense for less cost than phase dragon. psion is weaker defensively than immortal, but provides for a mechanism that may provide better offense, but with the drawback of potentially damaging their owner. if anything, i would think they would function well together in a deck with dim shields, or separately in other decks.