User blog comment:IamJakuhoRaikoben/Chapter 476: Bid Farewell to the Mage Girls, Review./@comment-26389992-20160308030703/@comment-4829046-20160308100546

Or... well.... yo know.... Mashima created the manga with the idea that Dragons are the supreme entity to the point where they need to be considered extinct for the story to progress. It was about how a boy was chasing after a creature that many considered to be a myth/legend. Gods were added much later simply because he needed something on par with the supreme entities. Demons were originally just a joke in most cases where they filled the typical fantasy monster spot. It was only when the series started picking up that all these other things came into consideration. From the getgo, Dragons = supreme entities and Dragon slayers = strongest warriors on the planet.

It isn't about 'making' them overall strongest, they always were. :P