The Math for some of this thread is here: http://www.mmo-champion.com/threads/...1#post19907234
Here is a summary of what priests are like at 5.2 relative to the start of MoP
1) PoH is nerfed to 96.75% of what is was at MoP start, and it can no longer be used to stack aegis. This assumes a re-itemization to crit/haste. This is a theoretical value only because crit has a lower than maximal value due to overheal. So in reality it is even less than that. Reitemization to haste only however can keep the HPS at roughly 94-95% regardless of overheal, but that is sensitive to mana regeneration.
2) Spirit shell is nerfed to 80% assuming reitemization from high mastery to haste or crit or both. It now scales very poorly with mastery, but extremely well with crit, since crit scaling is 2+mastery.
3) Rapture was nerfed noticeably since it is again 150% of spirit, but now it does not include temporary spirit procs.
4) All spells had their mana cost reduced by 10%. PWS cost was reduced by a furhter 25% so 67.5% of the mana cost it had at the start.
5) All heals now apply a 50% aegis on crit rather than 30%, so the scaling for crit changes to (1+crit*(2+mastery)) instead of (1+crit*(2+0.6*mastery)). Assuming a re-itemization to crit this is a theoretical buff of 10%. This is a theoretical buff because of the behaviour of crit discussed above. Reitemization to haste only produces a slightly lower buff that is insensitive to overheal but sensitive to mana regeneration.
6) Penance was buffed to 120% on top of that so a total buff of 132%
7) Binding heal was buffed by an additional and multiplicative 50%, so the overall buff is 165%.
8) Solace was buffed to a level above mindbender
9) Holy fire was nerfed by 33%, since its cast time is now 2s and can't be reduced.
10) Cascade was buffed by 25% and divine star was also buffed by an amount that I do not know.
Basically blizzard in 5.2 not only reverted all buffs to PoH, they actually nerfed PoH and spirit shell further. Disc no longer has a reliable away to add stack absorbs like paladins do, except with spirit shell on a 1min CD. Mana regen is roughly at the same level as it was at the start, but spell costs are cheaper and for PWS much more. All single target spells were buffed and binding heal and penance were buffed even further. Holy fire was nerfed for atonement, but the nerf can be reversed by choosing solace, which has better return than mindbender anyway.
Personally I think that the nerfs will make disc not viable once again and now we don't have the main thing that give disc additional utility. We no longer have the ability to stack absorbs. I don't know who thought this would improve disc, but I definitely they that he or she is an idiot.