I have heard that the person doing spell design does not want to add any additional Complete Heal/Percentage Heal spells for any of the Priest Classes.
To be honest, a Complete Heal is really only useful on raids in a CH chain. For normal healing in groups, even the clerics seem to mostly use their quick heals and Heal over Time spells. While Complete Healing is very mana efficient (at least for them), any sudden damage spike due to bad luck can cause you to lose a tank before the heal lands, at least in challenging content.
I'm basically happy with the quick heals we have. I do feel a little gypped that Clerics have stronger HoT spells, given that we had them before any other priest, but at least ours are the most efficient.