My response was that lighning phase could be done with both specs (which means it is no problem for disc!), since spamming glyphed binding heal would be enough on its own, you don't even need to move unless a ligthning strike targets you directly in which case you just use one of your on-the-move options.
Note how nowhere did it say there was no advantage to atonement or spirit shell in this fight. Neither did I state PW:S was of no use.
I didn't state they where useful either, but that is because I thought it went without saying that a disc priest would use them.
The raid dying when only casting atonement spells is obviously (I hope) a generalization that applies to most fights but not to those with huge buffs to atonement.
You can kill heroic Horridon never casting anthing but atonement spells, but if you exspect that to be the case for all those encounters then the rest of your healing team most likely doesn't really need you to meet the requirements.
The same is true for holy and PoH/CoH/PoM, you can win fight with them but you should exspect to have to use other spells, too.
The difference is: You don't have to constantly keep track of the fight like disc does to preemt damage. Reacting is mostly enough, thus I find it is much less involving.
So my opinion is that I can be more laid back playing holy.