They are the toughest thing in the game for me to beat, and they don't attack too often.
Errr.... your imagination maybe?
Because they are clearly one of the easiest enemies in the game (master dif, no breaking the game of any sort, takes 1.5 breath for me to die)
With my mage it goes like this - hit hit hit, dragon breathes i take cover, hit hit hit, dragon breathes i take cover, hit hit hit dead. Not to mention that having a summon up and you don't even need to take cover. They are more like target practice.
With my warrior it's a little harder (since i've tried to keep my weapon damage at bay with the enchantments) and it takes a bit more time than the mage but it's still quite easy.