Actually, considering how the Elemental Chaos in 4e is a wild mixture of all elements, I'd expect the power source to be likewise. Pure elements are the exception, not the rule. I was actually surprised pure elementals finally turned up in MM3.The more I think about the elemental power source, the more I want classes broken up by element.
Earth=defender
Water=leader
Fire=striker
Air=controller
The more I think about the elemental power source, the more I want classes broken up by element.
Earth=defender
Water=leader
Fire=striker
Air=controller
Just break it up like Codex Alera does, and go to town. I never confused their furycrafting with D&D style arcane magic.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.