Burst calc is way off. Premade pvp vs premade pvp lavaburst crits for like 15-17k... its like 35% damage reduction. So it would be more like... 60k for the 4 shaman, which is about 1/2 the life of someone. Not including overload, which is another reason i think mastery and lava surge are so important.
This is demonstrated in a few 85 pvp videos you can watch on youtube.
35% damage reduction is ridiculous.