David, I don't know what you're reading, but I highly recommend
www.theoi.com on Greek mythology, a compenium of original sources; or an earlier book compendium, Robert Graves,
The Greek Myths. On ancient goddesses who got "demoted," or whose functions were usurped by male gods, see Tikva Frymer-Kensky,
In the Wake of Goddesses. On Babylonians, Gavin White,
Babylonian Star Lore.
As you know, the gods' myths and functions could change substantially over time.
The Sumerian goddess Nisaba evolved (devolved??) into the wife of the Babylonian god Nabu, who basically took over her primary functions. He assimilated to the Greek god Hermes, and from Hermes to Mercury, not Apollo.
Apollo was not notably a planetary god until he took over from Helios and Phoebus.
Regardless of whether the constellation Aquarius "bears" or "pours," it had nothing to do with the founding of ancient astrology.