I enjoyed the elemental wheel in 11, though it would get me in a lot of trouble in parties. In any case the elemental wheel would cause unneeded problems. For instance, blms would never be allowed to fight ifrit HM or extreme because their major damage spells would be useless. It would require a complete re-working of the class/job that would bleed into conjurer because they have stone/wind spells.
Besides that, there are lore reasons for the spell split.
In any case, while the elemental wheel was fun, mmos have progressed to the point where it has become a needless hinderance in games with more than enough complicated mechanics as it is.