Predict some Magician changes.

Make HS available to AMs. (so they are wanted in party)
Give new attacking skill((s) to Bishops (so they can be attackers like AMs)
A skill to turn mobs weak against their elements. (so they can be as strong as other classes)

Giving one of the things that makes Bishops special to AMs and giving what makes AMs special to Bishops is not a good idea. Specially since the problem with mages is not internal balance but balance when compared to other classes. Making three different classes (well, the two AMs are already not that different) into 1 single class kills the purpose of having multiple classes.

Making all classes exactly equal is the best way to balance but having indistinguishable classes in an MMORPG is not good either. They need to be quite different and yet equally useful/wanted.