The way a Job like Geomancer can happen lore-wise is similar to how we got Astrologian: While in Japanese Sharlayan Astrologians are different from Ishgardians, they share the same name in EN and the quests revolve around how Sharlayan and Ishgardian Astromancy is different. GEO could very well share the name in another region (say, the New World) and be mechanically different while thematically similar. That said, I do agree that WHM/CNJ is already very similar to GEO, what with taking their powers from Nature, so there'd need to be heavy reworkings to make it feasible and have its own identity.

Also, please don't have them have to physically be on top of stuff for their spells, there's already too many players who haven't grasped not to stand in the bad.