User blog comment:IamJakuhoRaikoben/Chapter 476: Bid Farewell to the Mage Girls, Review./@comment-26389992-20160308030703/@comment-7418318-20160308135418

That's western gods (as in west of Japan).

In Japan itself Gods can be as tiny and powerless as what we in the west would call Spirits of Nature.

Just take a look at Mononoke-hime, there the "Gods" were giant animals, some with supernatural powers, but others just bigger version of normal animals with the ability to speak.

If you go by such believes, it's only natural that a Dragon would be stronger than a god. Just because Mashima is borrowing names and direction of powers from the Greek pantheon, doesn't mean they ARE the greek goods.