I'd like to get a bit of discussion going on Prayer of Healing. I don't seek to state any iron-clad conclusions so much as get the issue out in the open and discussed.
I believe that Prayer of Healing is too effective in Ulduar. Prayer of Healing is a niche spell, like most Priest heals. It is super effective in its one area of expertise (high single-party damage) but otherwise not very good. So far this hasn't been an issue, as most content hasn't catered to it. However now we enter Ulduar. Ignis, XT, Kologarn, Auriaya, Hodir, and Mimiron all pour large/predictable amounts of damage across the raid. Iron Council and Freya also will often dump damage that is very favorable to PoH. The number of fights where PoH will not be a dominant heal for a Holy Priest are small.
Is this so bad? Before many Priests didn't bother putting PoH on their bars, and now it gets to shine. For the Priests themselves it's not problematic; anybody who just spams PoH like you could CoH at the end of BC isn't going to heal properly. However I do wonder about its negative interactions with other healers. Group healing is usually a group effort - you have to save those in danger, stabilize them, and then finish topping them off. Most healers are proficient at two out of those three, but Prayer of Healing manages to do all those roles at once (CoH and PoM mopping up the rest). Whenever I'm on my Priest I can just handle massive AoE damage on my own, without having to work with other healers to get maximum benefit; I bring all the tools and I don't have significant enough mana restrictions to require holding back.
So, given this let's ask: should Prayer of Healing be nerfed? And if so, what would be the best manner to approach such a nerf?
We could just concede that T8 content is just PoH friendly, nothing more. The spell isn't at fault, it's that there are just so many fights that its niche shines in. This could very well be a temporary phase. Blizzard could change the nature of AoE damage in T9, or they could follow through with some of their suggestions on making tank healing more interesting and so shifting damage there (a role Holy Priests are not adept at).
If we don't accept this (either we don't want to wait, or we don't think the problem will go away) then there could be a few ways of approaching a PoH nerf.
a) Sustainability. Blizzard has expressed already that they aren't confident the regen nerfs of 3.1 were enough. This could just be a result of that. PoH's major limitation is its mana cost (in theory) and without that it takes over. Even if general regen nerfs aren't incoming we could hit Healing Prayers, although my own Priest doesn't even have that talent and still manages to use/abuse PoH as much as she likes. I would be hesitant to increase the mana cost as this would have a knock-on effect on Disc, which doesn't particularly need its AoE healing nerfed.
b) Throughput. We could just make PoH heal for less. This would also probably help keep it from being overly dominant as a niche heal. The problem here is just that however: if your heal isn't really great in its niche, then why cast it? I can't speak for all Priests, but I like the feeling of going to use PoH and getting a visceral sensation that you're pulling out The Big Guns. If we nerfed it down so that it's just CoH with a cast time, I'd be afraid that you'd lose what made it fun/good to cast in the first place.
c) Cast Time. We could give PoH a longer cast time, then perhaps buff Serendipity a bit. You could make PoH a four second cast rather than three it would make it fairly cast-time prohibitive without having a few stacks of Serendipity, which would moderate spam-casting. My fear here is that you do lose the option to repeat cast. I don't think it's a problem that PoH can be repeatedly cast, it's that you can do so with impunity to the cost. Just making it so that you never want to cast two PoH's back to back seems like it would be a lame solution. Also similar to the above cost-increase issues it would make PoH supremely unattractive to Disc, which given its limited AoE healing options would feel like an unfair casualty.
d) Retooling. We could just change the spell in some fashion other than adjusting the numbers but altering its functionality. A limited example would be to do the following (numbers totally made up):
-Reduce the healing PoH does by approximately 20%
-Change Healing Prayers to increase the crit chance of PoH by 10/20% (like it once did)
-Chance the PoH glyph to reduce the healing PoH does by 15% but increase its bonus critical healing by 100% (so it heals for 200% on a crit)
The aim of these changes wouldn't be to reduce its average power so much as make PoH's healing uneven. You would go to heal a group and it would top off some members with huge heals, but leave gaping holes on others where it didn't crit. This makes it unattractive to cast PoH repeatedly on the same party and would work more intimately with healers like Shamans that deal with uneven damage.
Again, this is just an example I spun out.
As I stated at the beginning I haven't set out to prove much of anything, but instead to generate some thought on the topic. I pray that this thread doesn't fall into flaming, but one can only hope. I would especially appreciate any feedback as I plan to post this on the public forums at some point and would love to refine it further before that point.