"Damage Dealer in Water" made water magic a must-have, while air became useless. Maybe we need Damage Dealers in air and water, and Tactical Perks in fire and earth?
Regarding copying Damage Dealers into Air, we've already thought about it... we haven't come to a final conclusion. Air will definitely be strengthened, but Water will still be a priority - preer, dispel, and bless are significantly better than haste. That is, Air will make sense to take only if Water is not available, and for certain hero classes to whom it is rarely given (demons, for example).