One rule is still missing:
Ancient-Ones should not be able to use weapons and (especially!) vehicles. I think if any support is needed for half-god?
Please imagine one of my games where main character was: Cthulhu in Patrol Wagon with 2 x 0.45 Pistols. Lot of, lot of fun! Please just try to imagine the scene...
Well, they don't represent the actual ancient ones. They are a mere aspect and reflection of that ancient one's power. If you would have the actual Cthulhu in the game, you probably win. It's just an aspect of the AO's, which might take the shape of a tiny avatar or possessed cultist.
And yes, Cthulhu is famous for doing drive-by shootings, dressed in heavy furs.