I don't think Luna and Celestia can be considered gods, being able to move the Sun and the Moon doesn't make them so, and just like many said before, there was a group of unicorns who were doing so before them. Moving the sun, for exemple, isn't equal to be able to turn into something of 6 thousands to millions of °C or something. They're just more powerful than a group composed of unicorns and Star Swirl The Bearded which I think, even if he's less powerful, was a lot more skilled than both of the princesses