Let's keep our elemasters as the "lesser aides", and work on the greater elemasters as the "high-ranking" ones. Or we can just choose to NOT conver the high-ranking ones, and put a note in the flavor text of our conversion that such beings exist, but are greater deities and probably beyond stats in most cases.
Thoughts?
I think that there is some confusion about the structure and organization in Frank's Immortals Set, so let me see if I find out where the confusion begins:
1) The Immortal Hierarch is similar to the Deity Rank system. Ie Eternals and Hierarchs are equivalent to greater gods, and a Full Hierarch is the equivalent of a DR20.
2) Hierarchs (as well as all the other ranks) are subdivided between Novice Hiearchs and a Full Hierarch (ranked 0-6) .
3) Elemasters are level 2 Hierarchs and they and every immortal in that sphere report to the Full Hierarch (hence the wording "High ranking aide to the Full Hierarch). For example: The Elemaster over Fire, reports to the whomever the Full Hierarch is over Energy. The Full Hierarch over Energy leads all immortals in the sphere (former humans, elves, etc.), as some of the Full Hiearchs were once human at one point.
4l) Elemasters are NOT elementals or elemental Rulers. They are immortals. All immortals were once mortals. Just like the immortal Ixion is not a human (anymore). And because they are immortals they are still consider "outsiders", even though they make there home on an Elemental Plane, just as some deities also make their homes on the Elemental Plane (or even the Prime Material Plane)
So in conclusion: The highest leader of the Elementals are the Elemasters. They are not "Lesser" anything, unless you mean less than a full Hierarch, which is equivalent to comparing a god of DR20 to DR 18. There is no "Lesser Elemaster" and "Greater Elemaster). Elemasters are not Elementals, anymore than other immortals the same creature they used to be as mortals.