Same with metalbending: earthbending doesn't control metal for some reason, just the complex minerals leftover in the solid metal as debris. I am sure the GM has some explanation for their delineation that both ties them to the original style while still caching them as essentially separate entities.

At least I sure hope so.

EDIT: Dear god I just realized the GM added my revised opening post with the suggestions left in. Masaki, you should probably edit out the (add stuff here) comments.