Doma in general is also quite different in XIV than in VI. It wasn't transplanted directly into FF XIV. Other than Cyan's theme being used as Hien's theme and Cyan being a samurai ish character there really wasn't much linking them aside from the name. Doma Castle is a dungeon but didn't really make me think of FF VI's doma castle. The Delta/Sigmascape bosses at least have the benefit of being simulations based on other worlds, and not things from FFXIV's world.