I don't know, I think a separation of leadership duties and breeding is a good idea. If you mix the two, you get the chance of some tyrannical shenanigans. I wanted to draw a comparison to what Gilgamesh did to his people, but I guess he just abused his position as king to sleep with everyone's wife.
Different societal structure though, I realise that. I just don't think it's that far-fetched for a Tia to be in charge. Then again, it's more likely that it's run by the women.