I haven't yet read the Xerxes post/s, but generally:

1) A divine being's presence can help create things which may be slightly more advanced than normal for the civilisational stage, i.e. Lifprasil and his city, army, advanced armours, weaponry etc.
2) A divine being's presence can't cause the above to occur overnight. Even quick growing empires (i.e. Alexander's empire) took a good decade to establish militarily, and we're not even at that stage yet.