Pretty sure when it comes down to it Pyro just does more DPS plain and simple. Although I've heard AP can come close to Pyro in PvE in terms of DPS, it suffers in PvP for two main reasons. First, Pyro has a much bigger burst which is extremely important in PvP. Second, one of the key abilities of AP, the buffed flamethrower isn't very useful since it can be avoided/cancelled easily (not to mention you have to stand still). A lot of the talents are really good imo (such as the AoE/Stunned damage reduction or the movement speed skill) for PvP. Just needs a few buffs here and there.