This doesn't make any sense to me. Every unit can be killed in a variety of ways. Part of the point of the Seer Council is that they can be killed in fewer ways than the vast majority of other units. 3+/4++ or 2+/4++ rerollable with the speed to get away from the things that really can threaten them makes them extremely bad targets. If my opponents are shooting at my seer council and killing few or none of them, I'm winning.