Board Thread:Questions and Answers/@comment-24159861-20131123112708/@comment-21371438-20131123225705

Basically, the "Dragon" element is an ANTI-dragon element, as the element is commonly being used to slay Elder Dragons and -usually- rathian and rathalos, that are quite the flagships and usually promote the image of the classical wyvern (Rathian even have poisonous tail) or Lagiacruses -that promote classical sea serpent figures-

such element is known to exist in the Dragonfell berries, wich is the basic of Stygian Zynogre's power to manipulate such element, being able to manipulate thunderbugs that usually eat these dragon-bane berries

Like in the pokémon phenomena, it's said that feys (fairies) can manipulate powers able to kill dragons, despite not being presences of feys in the MHverse, we can kinda see some weapons (Magic Amulet - Hunting Horn) and armors (Rhopessa) which has impressive dragon elements bonuses, suggesting this.

Other possible theories might be that the dragon's soul is stored into the blade (some Deviljho weapon descriptions even suggest the weapon is still alive ) and you're using its strenght to combat other dragons

aside from all these stupid theories one fact is obvious: The Dragon Element should be your best choice if you aim to be a dragonslayer (...or Slime, slime always work, killing the fun of the epic explanation i gave up there, lol)