Priests have 2 different approaches to healing but one approach to pure dps (with the ability to go back to emergency healing).

Warriors have 2 different approaches to damage and one to tanking. Yet, you can also find that the “tank” tree can be efficient at DPS if specced for dps.

The Death Knight class is a very interesting move from Blizzard : their 3 talent trees offer benefits to both tanking and dps, but you have to choice which one to take. So there are like 3 options to take as DK, and 3 options to DPS (maybe even more if you count some cross-tree specs). In raid some are more searched for than others, because they are considered doing the most damage or taking the least.

You got 2 aspects to specialize a character : Gear and Talents.
A Paladin specs for DPS using a DPS gear, is nearly as efficient as a Pure DPS class. A paladin specced for tanking with a tank gear is as efficient as any other tank class.
A dps paladin in dps gear CANT tank. Ok he can taunt the mob to him, cast some protection spells and hope survive… it won’t last more than 5s against a raid boss.

Now, a DPS paladin using tank gear, or a DPS warrior using tank gear, can tank… but that will be much harder for him to survive, and for healers to heal him than if that was a paladin tank. Same a paladin tank in dps gear will be crushed too fast.

For a raid, what does a hybrid class offer : not much. They have tools that can save the day (like a melee dps druid can still combat rez, but they have 6k mana where their main heal eats 1k to give 4k health back to a 30-40k life tank… a melee dps druid can heal himself once or twice to save his own hide if healers are under pressure). The hybrids that can seriously help, are the DPS caster specs of classes that can heal : they won’t have the mana regeneration, the fastest heals, but at least they have mana and their spellpower affects both damage and healing spells. So a moonkin or elemental shaman can switch to healing role, in middle of a fight to.. “save the day”. Yet you won’t replace all your healers with elemental shamans, because a shaman restoration is still more efficient. Also DPS melee classes in DPS gear can switch to tanking stances and hope to save the day. They won’t have as much avoidance, or the skyrocket high life pool, or all the “oh shit buttons” but they can still sometimes save the day. In practice it means you might bring 2 pure tanks and 1 dps that can tank in a 10 man raid, instead of just 2 tanks, for additionnal safety.

Outside of raid, that’s a totally different discussion. A tank gearing for dps can go farm or solo quite some stuffs. Their killing rate will be lower, but their might break through where pure dps class will die (“elite” mobs).

In 5-man small instances, DPS specs geared for tank (or heal) can do very nice. Yet its easier with a pure spec… except if your outgear the content.

In WOW, Hybrid class rarely mean Hybrid role. You won’t replace all “pure” classes with “hybrid” classes. Because a spec remain a pure spec.
In raid, you know how many of each role you need. Its 2 tank, 2 heal, 6 dps for 10-man f.e. Sure its nice to have a 3rd capable of tanking or healing, just in case, especially for the first attempts, but will you bring 5 tank-capable, and 5-heal capable ? no.

Also, each class brings differents buffs and tools. Mixing the class is strong. The Hybridness of a class even means a larger choice in what you bring in your raid : Heroism is a strong buff that any Shaman can bring, but you don’t need to make one of your two healers a shaman, a shaman dps can just do.

There also are “pure” classes you hardly can skip : hunter or rogue. Both pure dps class, can seriously increase your tank threat, can safely initiate the pull. If you don’t bring them, that’s slightly harder.

Hybrid class often have very poor choice of spells for their role. Feral druid tank have 4 main attacks, 2 of which can be considered situation dependent (yet most of the time rotating both brings the most benefits). Warrior tank have like 2 more attacks to choose from based on situation, and also have abilities quite unique like reflecting spells, interrupting a spellcast, etc.

It’s all about tools, options, and playstyle. There is no class that can do all better than any other. (well there are some “exception”, if you see the DPS a DeathKnight ou Druid TANK can do in TANK gear in 5-man instances.. you sometimes wonder : do I really need a DPS ? but they do that much because they AOE, damage done to them increase the resource they need to ditch damage, and are getting healed, two druid tank wouldn’t work as good)

Exactly: dual talent specs.

Classes like druids & priest will even be able to dps/heal without having to regear (much).

Any mage can Frost Nova, Blink, go Invis, or Ice Block to get themselves out of sticky circumstances. They have a variety of AoE options, and have spells encompassing three distinct damage types.

A balance druid may have some armor to survive a hit, but is likely dressed in a fair bit of cloth, and not stacked for stamina, so it often won’t survive more than three. It has one AoE spell (albeit powerful barring nature resist), and loses DPS and function if it excludes *any* of its damage spells from its rotation. If use of one or two of those spells are limited, DPS takes a significant hit. On the other hand, a moonkin who is aware of their off-spec abilities can CR a fallen tank, shift to bear, taunt whatever’s loose, hit frenzied regen and hope to survive the tank regaining its bearings.

Same goes for the Priest. If he’s not the best healer in the game, then what’s the point in picking that class over one which is more versatile?

You want a one to one tank healer? Pallies are considered the best.
You want Hots? Talk to a Tree.
How about raid healing? Shammies excel.
And the jack of all trades? I think that’d be a Priest.

Each one of these classes CAN do each of these jobs, but there are certain classes that do it much better and easier than the others. So, there is not one uber healer class, which allows for a nice variety, imo.

Oh that’s an easy one: because within the scope of a single raid, a hybrid won’t be flipping roles AND beating out the pure classes. That warrior will tank like a pro, but his DPS will suffer badly (even in dps gear/stance) unless he goes and respecs.

Full discussion here:

http://teethandclaws.blogspot.com/2009/01/hybrid-envy.html

You’ve got it all wrong. Blizzard has mentioned more then once that they want the 4 classes to be able to tank end game content. Each tank does have a bit of a niche, being better at AOE tanking, threat generation, mitigation, avoidance,… But any class can tank Naxx.

All classes can also do roughly equal DPS. I’ve seen druids, DK, warriors in top 5 dps (still have to see a good DPS pallie).

As a matter of fact, I think the question should be turned around:
“If all hybrids can do equal DPS to pure DPS classes, what’s the point in bringing pure DPS classes”?

And if all warriors can just take a second spec to tank, so can my DK, someones druid or someones paladin.