-Spoilers for The Dragon's Eye-
Just rethinking some stuff here, is the Dragon's Eye really the best token? Sure it has the potential to "flood the world", but just how likely is that to happen? I can imagine coastal cities easily devastated, but what about those farther inland? Do you realize how much water it would take just to flood one continent? The bond tokens are still hard to control - after all, Rollan struggled just to create tunnels with the Heart. In another way, if you ranked the bond tokens by world-destroying powers, who's to say that the Heart couldn't create a continent-splitting earthquake? Or the Stormspeaker an ultimate hurricane?
In another way, to use the Dragon's Eye, you'd need some kind of water source to manipulate. Thus, you'd have all the advantage doing battle at sea, but less so on land, having to rely on rivers, lakes, etc. - that is, if there are any nearby. And just how many different things can you do with water? Waves... floods... any other battle moves? My point is, the Dragon's Eye isn't the most versatile token, or at least, I can imagine so much more being done with the other tokens.