The forums of the famous Horde raiding guild Elitist Jerks are home to possibly the most intelligent, respectful and creative WoW micro-community out there. (Amusingly, their Alliance counterparts, Death and Taxes, have one of the most vicious and mind-numbing forums out there. Coincidence?) They're deep into theorycrafting and gear questions, so it should come as no surprise that they've created one of the most intriguing threads about caster itemization I've ever seen.
Basically, according to Mearis, the BOP crafted tailoring sets -- Primal Mooncloth, Frozen Shadoweave, and Spellfire -- are actually superior for raid DPS and healing to Tier 4 and 5. For example, here is the Tier 5 priest damage gear, compared to the Frozen Shadoweave Vest. The Frozen Shadoweave offers significantly more pure shadow damage, and the spirit and crit on the Tier 5 isn't that great for shadow priests. A warlock I talked to also rated Frozen Shadoweave above lock T4, and checking out the gear in general, the crafted sets seem to feature nearly double the damage increase (for a certain class of spells) of the tier gear.
Mearis says this has two negative effects. First off, it makes tailoring nearly mandatory to stay competitive in early end-game DPS, and by having early access to seriously powerful gear, it allows mages, locks and priests to do much more damage than comparative physical DPS classes -- and leads to more nerf cries from rogues and warriors.
I talked to a warlock in the top raiding guild on my server who has the full Frozen Shadoweave set. He said that he considered the tailored items "amazing" and that they probably did contribute to cloth-wearers dominating the damage charts early on. However, he added that he noticed rogues and warriors catching up to mages and locks in damage as they began getting more pieces of their Tier 4 and arena gears, while the clothies weren't replacing their BOP crafted sets yet. And since tailoring was pretty much a money pit before TBC, he didn't mind that it was now suddenly powerful for raiding.
"I'm not ready to jump on the bandwagon and say that the crafted is overpowered because it is expensive to make and may be replaced as early as 4-piece Tier 4," he said. "And I'm happy to see tailoring be a worthwhile prof while it lasts." Plus, the caster pieces don't have a ton of stamina, which is important on certain boss fights. A shadow priest in my guild with Frozen Shadoweave and Battlecast added, "They're not overpowered -- the T4-T5 sets are just weak."
Personally, I like the idea of crafted sets that are equal to raid sets, and think the tailoring clothes and the blacksmithing items are a step forward for the game. Now if only leatherworkers and engineers could get nice things ...