Well, keep in mind that Flash of Light is going to be filling a very different niche in the expansion. Generally, you would use it if someone needs a heal in the next 1.5 seconds or they will die, and Holy Shock is on cooldown. Since you can't always depend on Holy Shock, you need a baseline fast yet expensive heal to fill that role. It isn't intended to be something you use if you don't need to any more.