I didn't say 6|7, which is 6 attack. I said 6/7, meaning the regular health is 6, or 7 if upgraded.
It may have 14 health right now, but it has only 2 attack, costs 4/3 quanta (which is a much worse damage/quantum ratio than most creatures), and there are lots of non-damage forms of CC out there. Also it takes up a slot in your deck. If your opponent plays no creatures worth copying, this creature finds itself underpowered - this means if your opponent's fractaling scarabs, ball lightnings, or brimstone eaters, or using quinted critters, or running creatureless...
That's why the health was so high. If it's going to be so situational, it has to have redeeming factors as a standalone. But 6-7 health wouldn't be too much of a drop... upped, that's still three firestorms.