Hmm. The problem with a mono earth deck is anything with sufficient creature control could shut it down to make it strictly worse than a rainbow deck, though to be fair, that's true of pretty much every non-aether mono-deck.
I have no fundamental problem problem with switching the element, though thematically I think earth makes the most sense (and is fundamentally a matter of cost).
I'm open to more changes/thoughts, but I think it would be a cool mechanic if it could be salvaged and made workable.