Again, which holy can do better. Prep with a shield and a PoM. Disc can do this. Their shields Are better. Their PoM IS weaker. AoE hits. We CoH, PoH, PoH, CoH. What can you do? PoH is all you can do. All the while we can squeeze out more AoE healing, whilst our better PoM is pinging about.
The maxim has already been stated: Disc = single target and group healer. Holy = Versatile allround healer specifically AoE orientated.