Ye i think you have to wait till you get rank 2 heals before you see how well they heal. At least thats what I have heard. I think Tempest of Set is an AoE healer, although i could be wrong.
Herald of Xotli is probably going to be underplayed because its a strange class. Basically HoX is a caster+melee dpsers. They use the demonic powers to turn themselves into demons for short periods of time. My only concern about this class is what the play style will be like. Will they be a caster until they turn into a demon and then run into melee for a short time and then go back into caster mode or will they be pure melee dpsers.