My concern is not power but flavor. I know airships are powerful, I used them by myself, but I wished there were more such cool units as the airships for the Kuriotates. They should have some late game powerhouse by their own to have something to research, what you really like. Chalid and Empyrean Priests anyone can discover, but what do the Kurios get Centaurs, Centaurs and look more Centaurs. The airships apealed me not because of their power, but because of their style.
And that's why I'm saying give the Kurios more cool units like the airships. Flying units could be a unique factor for the Kurios.
Griffin Riders could for example be build with animal handling with a strength of 7-8 and a movement of basic 4, but you need a caught griffin, wouldn't be too powerful, but cool. You could give them the same with rhoks with a lower strength, but buildable without a caught unit. I think of all the fantastic RPGs, where you were riding on a giant bird.
A sphinx could come with strength of will or with omniscience - I don't which fits it better - and should have a low attacking power and a high toughness. Spirit III, Life III and Soul III regainable I already suggested. A new idea, that occured to me, was, that it could sacrifice itself to build a unique building "Wisdom of the Sphinx" (that is a Sphinx that has settled down) which gives you a great research bonus and GP-bonus in all of your cities or something like that. Note that the myth of sphinx is egyptian AND greek, so it would fit the Kurios, which have a link to greek mythology
Another possibility would be to make the Sphinx a unique feature on the map, which anyone could visit. The original myth of the Sphinx says that she gave you a riddle and if you can't solve it you will be choked to death. In FFH it could be implemented like this, that she gives you a task and if you perform it during a certain time (let's say 20 turns) you will get a golden age or some kind of permanent bonus, otherwise you get punished (For example 5 turns anarchy - compared with Ilian Worldspell quite fair

).