It’s a pretty touchy and frankly, ugly subject right now. With the mass merging of raid buffs, the typical raid composition has been tossed out the window and there are many more opportunities for the average raider to find a spot come Wrath of the Lich King.
Our goal was not to remove anything unique from the classes. Our goal was to get rid of anything that was considered so mandatory that you would consider scrapping a raid without that player. A great example is Bloodlust / Heroism. Raids were absolutely stacking shamans to do a rotation of these spells to the extent that we designed encounters assuming that would be the case.
A slightly different example is Illidan. That encounter assumed (because it has been changed) that you had a warrior in the raid, and that the warrior was tanking.
On the other hand, we didn’t design any encounters for LK with the thought that “They’ll use a death knight here to pull,” or “The druid will use Rebirth here,” or “You have to have Spell Reflect or you’ll wipe” or “The rogues need to disarm the traps in the Suppression Room.” Now all of those spells do have their uses and will make certain encounters easier. If those spells were of questionable or no utility then the class distinction really starts to devolve into damage, healing and tanking. But none of them should be mandatory. I don’t think most guilds will call the raid if they don’t have a DK for Malygos the way most guilds *did* call the raid if they didn’t have a hunter (or two) and a mage for Maulgar (pre-last patch anyway).
There are a few encounters we’re keeping an eye on. Naxx 25 still has an encounter that requires 2 priests. That is probably a safe assumption for a raid of that size, but it’s a slippery slope. If we had required 2 Shadow priests, for example, it would probably cross the line. (And no, we won’t start implementing encounters like that when we allow dual-specs.)
I also realize that some players (particularly those who don’t play the class in contention) will argue that Rebirth or whatever is so powerful that raids will require a druid. Maybe there are some out there that do. A lot of these decisions are judgment calls on our part, and as I’m sure you all know, decisions on the part of raid leaders, especially inexperienced ones, can sometimes be misinformed. (src)
I agree that this does cause issues. If your class buff/debuff can be covered by another, and that class can always tank/heal/dps better then your class, then your SOL buddy. Welcome to the endangered species list.
Unfortunately all Mages bring is Arcane Int (which is a raid wide buff so only one Mage casts that every 60 mins) and spell crit (via Fire or Frost talents). Couple that with not being the highest on the DPS charts compared to other classes, all we have it crowd control. And even that is handled pretty well by other classes.
Maybe this will all change in Wrath but as of right now, I can see why Mages might be under represented in raids.