I'll just say that air, earth, water, and fire have unique advantages that are specific to them, and if these advantages are logically arranged, they will balance all the schools:) in the sense that the player can choose their priorities, whether they want to be a master of air, earth, water, or fire. IMO, this would be more logical and also better for the gameplay. Everything is interconnected, and there should be a clear, albeit fantastical, logic in everything. There would also be rivalry between the schools, rather than their mixing, which, IMO, would be more interesting.
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"So much has gone
and little is new"
David Bowie