That is true but with a few exceptions. Only about a quarter of the nation's Magice is traded to other countries, the rest is used by the tribes themselves and the Belphradunn and Arathyl Tribes control the mining and distribution of Magice and so they remain on an equal standing with the Truiets who need their Magice for their own needs. The Lobradis Tribe, while not as financially powerful as the other three have been able to maintain their high positon becuase they control the routes in and out of the capital and are the only tribe that can claim direct blood relation to the Jha'N (monarch) as the Uniter, the first and greatest of the Jha'Ns, was originally of the Lobradis Tribe.
Also trade ships of the Wanderer Caste returning from the south have brought with them The Enlightenment, and with it comes airship technology. Currently only the Jha'N and the Wanderers posses the only working airships in Evelakaia but this still threatens the power of the Truiets as airships can bipass their trade routes altogether.
Theres a lot of stuff about this world that complicates things and I don't want to bore people with the details just yet but hopefully this info helps to clear up the matters.