From experience, if a healer is ripping aggro, it's usually because they are spam aoe healing or spamming the tank, when there is no damage going out, then they don't even lucid. Then complain that they don't have mana. The damage in this game is so scripted that a Regen on a tank is almost all you need, and only aoe heal when damage goes out. For the dps, they probably think that diversion is some sort of dps loss or something, or they only use it when they notice they are high on aggro, this is when it's too late.