That's a pretty weak lore excuse. Like others said, we've formed bonds with demons, and beings that don't speak any language we understand. We've formed bonds with time-and-space trancending NPCs, we've done a lot of crazier things than bond with "empty vessels." And if they're so empty, how can they talk to us and interact with us like ordinary children of Vana'diel?Blue Mage stuff
Also in the blue mage quests, it is said that you are *like* an empty vessel (waiting to be filled with blue magic) when you become a blue mage at the beginning. Not that you *are* an empty vessel and will be for all time.