Fundamentally, PvE should never require any buffs/nerfs since AI does not change. You can easily balance one rotation against another fighting dummies. PvP requires balance against all other classes as well as the ever-changing nature of a player vs. player environment.
So much this. AI can always be scaled up or down to compensate for any kind of balance pvp goes through. Every mmo that has pvp should always base its balance purely around pvp.