Geomancer

[Archwizard]

(Btw, can we all stop forgetting that classic GEO technically had access to all elements through different Terrain/Weather and would thus be a prime candidate for a true elemental caster? Sure, FFXIV's version points out Earth/Wind/Water specifically, but seeing as Ishgardian Astrologians are very different from the AST we got I dont see that as an issue :P)

I don't think anybody was saying other elements are completely off the table – with the chambers of Swallow's Compass ending in "Heart of the Dragon" with a fire-throwing tengu inside, I could see a rotation built around cycling between Earth, Wind and Water to end with a massive Fire finisher (perhaps magma-based to maintain distinction from the fire spells flung by other casters), much as BLM and RDM build up to non-elemental finishers. Plus it could tie in well with the classical elements, even though Feng Shui uses the five Chinese elements (excluding wind, and including wood which has the same place, and metal).

If you mean all six though, I should point out none of the dedicated casters practice more than four elements – largely because more than three isn't really necessary for all practical purposes (hence why SMN has only 3 Egis despite six pure-elemental primals), and RDM's dual model essentially gives it clones of really only three spells. So while Ice and Lightning aren't off the table, they wouldn't entirely be unnecessary.