There may be another reason to having Gabranth on the cover, and it has to do with the ending of the game. Gabranth get's quite a bit of growth towards the end and their is an interesting plot twist in the ending...

As for it being (SPOILER)Venat, I wouldn't put it pass this team.

Tactics felt more or less like the rise of the Roman Empire, Vagrant Story felt like the Spanish Inquisition, and Tactics Advance felt like a Grimm's Brothers faerie tale gone horribly wrong-less violence, but much more dark.

So FFXII... FFXII sort've has a battle for the 'new world' thing going on, but it's much too early for me to say.
If I was going to base FFXII on an era of history, I would say it was like Alexander the Great's campaign to conquer Persia. But the New World idea works as well.