The damage of fire in PvP IS extremely low. Not sure how many spells are affected but I am sure that Pyroblast is. I hit for about 45k (crit) when on retail it would bit for more than double. I even made a bug report on it but was dismissed without any explanation why. Also keep in mind that the numbers are of people with less gear.
Please don't think of it as a whine post or dismiss it without an explanation as to why. I wish I could have the tables of how much spells would hit for, but that's impossible as many things play a role on it. So... Check the videos, check the numbers on the server and you'll see that it's way off.
Watch some videos, for the Fire burst rotation. If you manage to get it done properly you could easily burst someone down to 0, if he is on your gear, or even a little bit more.