Anonymoose, I'm not particularly inclined to get into a lore debate with you, but I want to provide a counterpoint.

For the Greeks, their mythology gave a backstory to many constellations, and in their mythology they weren't not just clusters of stars forming a particular shape, but a living, powerful entity watching, or haunting, the Heavens. Similarly, the constellations in FFXIV are associated with specific entities from mythology, although whether they recognize them as just being stars in a particular shape, or believe them to be actual entities/aspects living among the stars, isn't stated to the best of my knowledge.

Even today, astrology holds that the far distant stars have the power to influence activities and even destinies on Earth. Being a fantasy game, and what's more a Final Fantasy game which is even weirder at times, it's not outside the realm of possibility that Astrologians are in fact drawing residual aether from celestial bodies.