The key word there is "potential." I'll explain why this is problematic below.
The difference between Spain and Brazil is that Spain was a superpower. Ancient Rome isn't a superpower any more but we're not relying on modern history. With Brazil, you have to rely on modern history, so you want to make sure it's actually come true (the United States is a superpower, not "has potential to be" a superpower).
I agree that what you say is true. But at the same time the Zulu was included in previous civ versions and the Zulu have never been a superpower. In the 1800's, the rest of the world had guns, were bulding railroad transportation systems and many other things. The Zulu were running around with spears. And any guns they did have were given to them by Europeans, or they may have managed to capture/steal some guns from the occupying British. The only reason why the Zulu were included is because Africans like to pretend that they contributed just as much to civilization as Europe and Asia, when the reality is Africa has contributed nothing. In north Africa they have contributed (Egypt for example), but north Africa is more similar to the Arabs, just located on the African continent.
At best, Zulu was a regional superpower when compared to the rest of Africa. And Brazil is already a regional superpower.