Heretics are very strong in general. Their efficiency is amazing. With rituals, they are significantly buffed this age. I, personally, have always loved heretics because I know how nasty maintaining thieves/wizards is over a mid to long-term war, particularly if you are charged with operations against a province with significant NW protection. The absence of losses is an amazing boon. If I had to design a personality to screw with large provinces, that personality is heretic. (as ASF can recall I told him when they were first released. We had quite a long conversation about it IIRC.)