This is not uncommon. My locks are at about 550 +dmg and any competent healing class can easily outheal my DoTs unless I keep them CC'd or interrupted. Now, granted, I'm demonology spec, so that cuts down on DoT dmg dramatically. Round-robin deathcoil and felhunters are about the only thing that works. With shammies, I started killing healy druids at 48. :P