I think you're taking that a bit too literal. There wasn't a specific place where Alexander and Odin will fight, if I remember correctly (except perhaps the Alzadaal Ruins), and Vigrith is supposed to be a large field. While in Norse Mythology it is where Ragnarok takes places as a battlefield, in FFXI it could be just a large-scale battlefield that ties in with ToAU Lore, for all we know.