I beat the game, I like it but I don't know why anyone would buy a water tower when you can buy a nature and fire tower for the same price.
You're right! The water tower has the highest DPS by far, but the fire and earth tower hit damage breakpoints more evenly. We realized the cost difference should be closer to 40/50/60 for fire/nature/water, but it was too late in the process to rebalance the levels and economy. Thank you for playing!