User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-4361439-20130206182832/@comment-4933023-20130206185230

This is just me guessing, but a lot of games that come from Japan, the dragons are weak to other dragons, and not much more than that.

It's this way in Pokemon too (just mentioning this because it's from Japan), Dragon type being the only really effective type against dragon, besides ice. Yet dragon seems to do more damage.

I'm not sure if it's just Japanese mythology, or just a coincidence. More than likely it's just a gameplay mechanic.