sorry for saying it but don't you think suggesting a smite build in 1.10 is a bit obvious? if you remove the +15% shadow damage debuff and vamperic embrace in a pve setting then it's no longer smite vs mindflay+mindblast but smite vs frostbolts/shadowbolts/what not with the added benefit that you can do ok healing in your damage gear instead of doing damage if needed.

I wouldn't call Spiritual Healing critical, though it is definitely a plus. Improved healing on the other hand is very important, but some priests choose to spec into 10% mana instead (this build forces the decision). What I was trying to get at is that this spec is no where near as healer unfriendly as a 31 shadow spec.

This is exactly how I felt.

I was a pure PvE healing spec for almost a year. What happened is I never played my priest in anything but raiding and felt like I lost something with him. When not raiding, I'd go off and play my alts. Hell, I have a 60 warrior in Tier 1 epics since I dragged her along to Molten Core to take passed loot in order that I could have something I could farm with.

1.10 gave me the holy damage/healing hybrid. I respec'd 31/20 last week for and I honestly felt a whole new life back into my priest. I can actually go farm for essences with him while queued for a background. I can farm Twlight Cultists for templar pieces without feeling like a gimp'd class anymore. I actually enjoy playing him outside of raiding again.

I still have Improved Healing. I'm only missing Spiritual Healing in my build, and I think that's a fine trade off between raid utility and being able to actually enjoy my character outside of the instance portal. Not too mention I get to toss Power Infusion on a mage or warlock during raiding. It seems to be becoming standard to hit one when the mob is around 80% or so and they go nuts.

If anything, 1.10 made my priest pretty much the character I always wanted him to be. A hybrid class who can hold his own.

I'll expand on my original point: That priests can't do raid DPS because they have no mana recovery talent.

The problem with priests are that they have very attractive raid talents, be them the stacking shadow vulnerability talent to vampiric embrace.
A shadow priest is the way to go for raid DPS, if you so choose. why? Because in a main tank's group, the healing done by vampiric embrace is an excellent compliment to the damage that the priest does.

why is a priest good in shadow for raids?
1) You don't need +hit gear. You have a talent that makes your +hit% as high or higher than any mage, any warlock, any warrior. Shadow Focus is ridiculous.
2) since you don't need +hit gear, you can concentrate on +damage +crit gear. Since this is the case, and the fact that the majority of your damage comes from dot and channel damage, your efficiency of +damage gear is extremely high.
3) The increase that you see in your damage with shadow weaving also increases the damage that warlocks can output, increasing their damage / mana ratio, and increasing the speed at which good warlocks can down the tougher mobs in the game.
4) You are a master of your aggro. A priest not only has subtlety in their spells, but also has an aggro drop in fade. stop DPS, fade, and allow the tank to regain aggro. The beauty of fade is that it is UNRESISTABLE. A mob will ALWAYS bounce back to the MT when a priest pulls aggro.
5) Vampiric Embrace. With the very best +shadow and +damage gear that a priest can get, he can pull out over 500DPS constant (on paper, so probably a bit lower.), with vamp embrace up that's 125 health per second to everyone in that priest's party, which should include the main tank. The health per second takes some of the strain off of your other healers, as they don't need to constantly be casting quicker heals, as the HoTs they cast + vampiric embrace is enough to allow healers to all use slower, mana efficient spells.

Sounds pretty sweet, doesn't it?
but in practice, a shadow priest in 1.9 had a mana pool that lasted roughly 5 minutes. In 1.10 after the priest changes, mental strength and mental agility for the most part are out of range of the big damage builds. this means that your instant casts (90% of the shadow spells you cast) cost more and yet you're crippled by a smaller(!) mana pool than before. The inclusion of meditation into most shadow builds is GREAT for pvp, but in pve it doesn't add much at all to the priest's longivity.

How does this compare to a heavy disc build?
A heavy disc build priest can still heal adequately. They might not have the great talents of Spiritual guildance or Spiritual Healing, but they can still cast healing spells.
Power Infusion is great fun.
Divine Spirit!
HUGE CRITS OMG.

well, to be honest, a heavy disc build with the maximum amount of +damage gear needs a lot of +hit gear too, unlike shadow. this means that you need to sac crit and +damage to make up the difference.
Also, those big crits pull more aggro, and with no sub talent even possible (Most people don't take the sub talent anyway, but I would consider it if I had crazy gear.) the threat of pulling aggro becomes present. Fade works once, but when you blow Med and PI to hit with a 2200 HF you're going to get it right back.
Moderation would be the name of the game for a heavy disc priest, whereas a shadow priest can constantly cast.

A heavy disc priest does less damage than a warlock or mage, and doesn't have a talent like vampiric embrace or shadow weaving to help offset the loss of a healer.

Mental agility does almost nothing for a heavy disc priest, as most of their damage comes from channeled spells.
Mental strength is only a temporary fix, much like +22 int.

and finally:
Neither build has a comparable talent to Evocation, Spirit Tap, or Dark Pact. this means that druids will be blowing innervates on a priest to keep their mana up, which adds almost nothing to a raid, when that same priest could be healing and keeping a mage, which chances are they'll do more damage next patch, up and alive to continue a fight.

while the oracle set points towards the implementation of a heavy disc build in raiding, with it's resistance lowering and +damage, Blizzard at this time didn't seem to follow through and give the priests the chance at a mana recovery talent, which cripples raid dps priests.
Maybe sometime in the future a priest will be able to do raid DPS, but for today heavy disc and heavy shadow builds are restricted to short term pvp encounters and molten core.