Theoretically, with enough crit and spell damage, LOLSmite will beat out Shadow for pure DPS purposes, because Holy spells having better spell damage coefficients and good synergy with a Ret Pally and a mana battery. That said, the amount of extra DPS a LOLSmite Priest can do isn't significantly more than a Shadow Priest, but the utility is FAR less.
A LOLSmite Priest does bring a decent off-healer to the raid, and possibly IDS (so the other Holy Priests can go CoH), but that's it. A Shadow Priest brings massive amounts of mana regen, Shadow Weaving (increases all Shadow Damage, so great for Shadow Priests and Warlocks), Misery (increases ALL spell damage, so great for Shadow Priests, LOLSmite Priests, Warlocks, Mages, Shamans, Moonkin Druids, Prot Pallies, etc.), and possibly silence. IOW, what little amount a Shadow Priest may lack in personal DPS is more than made up for in buffing total raid DPS and whatever mana they bring back. Plus, the Shadow Priest can still off-heal if necessary, though not quite as well.
The only thing a Shadow Priest really lacks that a LOLSmite Priest can bring is IDS. A normal raid will probably bring 3 Priests (1 IDS, 1 CoH, 1 Shadow). For a LOLSmite Priest to make sense, you either have to bring 4 Priests to make it worth while (1 LOLSmite, 2 CoH, 1 Shadow), but then you're losing out on another class, which means you're losing one other pure DPS class, for the small benefit of one CoH priest over an IDS Priest. Chances are that the DPS from a LOLSmite priest is FAR behind what a pure DPS build can bring, like a Hunter, Warlock, Mage, or Rogue. So, in essence, you're trading several hundred DPS for upgrading an IDS Priest to a CoH priest. Now, CoH is nice... but not THAT nice.
Basically, LOLSmite is a fun build, I have more fun with that build than I do with Shadow, but it just isn't fit for raiding. It's a really good leveling spec, and good for 5-mans and even feasible into Karazhan. But that's about the limit of it.
A LOLSmite Priest does bring a decent off-healer to the raid, and possibly IDS (so the other Holy Priests can go CoH), but that's it. A Shadow Priest brings massive amounts of mana regen, Shadow Weaving (increases all Shadow Damage, so great for Shadow Priests and Warlocks), Misery (increases ALL spell damage, so great for Shadow Priests, LOLSmite Priests, Warlocks, Mages, Shamans, Moonkin Druids, Prot Pallies, etc.), and possibly silence. IOW, what little amount a Shadow Priest may lack in personal DPS is more than made up for in buffing total raid DPS and whatever mana they bring back. Plus, the Shadow Priest can still off-heal if necessary, though not quite as well.
The only thing a Shadow Priest really lacks that a LOLSmite Priest can bring is IDS. A normal raid will probably bring 3 Priests (1 IDS, 1 CoH, 1 Shadow). For a LOLSmite Priest to make sense, you either have to bring 4 Priests to make it worth while (1 LOLSmite, 2 CoH, 1 Shadow), but then you're losing out on another class, which means you're losing one other pure DPS class, for the small benefit of one CoH priest over an IDS Priest. Chances are that the DPS from a LOLSmite priest is FAR behind what a pure DPS build can bring, like a Hunter, Warlock, Mage, or Rogue. So, in essence, you're trading several hundred DPS for upgrading an IDS Priest to a CoH priest. Now, CoH is nice... but not THAT nice.
Basically, LOLSmite is a fun build, I have more fun with that build than I do with Shadow, but it just isn't fit for raiding. It's a really good leveling spec, and good for 5-mans and even feasible into Karazhan. But that's about the limit of it.