The intrinsic 'curse' of the hybrid is that you pay a penalty in DPS (if you choose to spec that way) in exchange for playing a class that can do something aside from DPSing. Whether or not you ever intend to do anything aside from hitting things with a 2h weapon or two is irrelevant: you could, and so your class is subject to an inherent cap that keeps its potential below that of a class like a hunter, rogue, warlock or mage. Sometimes the cap is very small and individual skill can surpass it, so that a hybrid DPSer who really knows his or her class, has the best possible gear, gems, glyphs and enchants and hits her or his rotation properly can actually surpass a 'pure' DPS class. For that matter, sometimes the pure DPS classes are held back by mechanics that don't benefit them. But nevertheless the cap is there.
It's important to note that this cap is only to keep hybrid DPS below pure DPS. In the current scheme of things in World of Warcraft, all tanks and healers are considered hybrids. Priests have a DPS spec and two healing specs. Warriors have two DPS specs and one tanking spec. There's an effort to make all three specs viable for PvP and PvE. Much as was the case in Burning Crusade, this expansion has had a lot of growing pains for the warrior class. It's indisputable that both death knights and paladins are more popular than warriors now. (It's also true that druids are as well, but it's also clear that feral tanks are on the decline and feral DPS don't outnumber warrior DPS specs. Druid numbers are clearly spread out between healing, ranged dps and two kinds of physical play.) But while death knights have gone up and down in popularity and power from patch to patch (as you'd expect a tanking class designed for this expansion) and paladins are clearly ascendant in both their DPS and tanking roles, warriors haven't really gotten worse per se.
The consequence to warriors of class role homogenization have been that other classes have gotten better and in so doing the appearance is that warriors have gotten worse. But this isn't the reality. Mind you, in some cases not getting worse is getting worse when other classes get a lot better than you are. We're seeing adjustments to how classes tank on the PTR and in recent patches for that very reason. Standing still is functionally the same as going backwards when someone else rockets past you. The problem here is perception. We often see two arguments bandied about. One is that because warriors are still overwhelmingly popular in raiding, warrior tanks are fine. The other is that because warriors are less numerous than other tanking hybrids in DPS or tanking roles, warriors are broken. (A subset is the 'warrior tanks do less DPS than other tanks while tanking' which we'll discuss as well.) Perception is a powerful thing, but it doesn't always tell you anything useful.
Why are warriors so popular as raid tanks if they're eclipsed in five mans and in general numbers of tank spec characters? If there are less prot warriors than prot paladins or tanking DK's, why are there more warriors as raid tanks? Are these warriors legacy tanks held over from previous expansions and older content who've kept tanking and have therefore kept their tanking roles in their guilds even as overall more and more players come into the game looking to tank but not looking to play a warrior to do it? Clearly this is sometimes the case. We know there are less protection spec warriors (the overwhelmingly most popular warrior spec is protection) than there are protection spec paladins, even though retribution, not protection, is the most popular paladin spec. But there are more warriors tanking raids. Ghostcrawler has repeatedly told us so.
Obviously some of those paladins and death knights are alts, as are some of those warriors. I myself tank on both a dk and a warrior. And in the interest of fairness, I much prefer the warrior.
I'm going to just come out and say something: warriors have lost a lot of players to homogenization, and it is in the best interest of the class that those players have moved on. Warrior tanking has issues, warrior DPS has issues, there are always elemental that can and should be improved. A buff to Vitality is a nice small change. A buff to Devastate damage was a nice small change. A buff to Revenge damage will also be a nice small change. While it would be nice for warriors to have a ground effect DoT like Consecrate or Death and Decay or to be able to spam Thunder Clap the way druids can spam Swipe, while DPS warriors are still overly reliant on gear escalation and stats like ArP while other plate DPS can stack strength more reliably and aren't shackled to a resource system that starts empty and builds up, we should look at homogenization as effectively battlefield triage. It's not, and it should not be, the first recourse to a class issue.
Trust me, you don't want Ardent Defender. No, really. The talent is simultaneously hideously OP and horribly broken. It's OP because it has no element of player control in it. The only decision you as a player make about the talent that can prevent your tank from dying is spending talent points to acquire it. You can't use it at the wrong time, you can't forget to use it, you can't make any decisions about it at all. And that is also exactly why it's horrible. If you're in a situation where knowing exactly when to use a cooldown is important... Algalon, Festergut, Putricide P3... Ardent Defender is worthless. It may have procced before you even got to the part where you'd need it, and if not, then it will proc once and be gone for the next huge burst of damage that will kill your tank. I'd much rather have Last Stand and have the choice of when and how to use it in my own hands than have the talent make the decision for me.
The homogenization factor must be carefully watched. It leads to clases feeling like pale retreads of each other. Pick an ability a class has that you envy and ask yourself: would I reroll for it? Would I rather play X class than this one? Clearly, a number of players said yes and moved away from warriors in Wrath of the Lich King. You hear a lot of talk about effective health and scaling and there are concerns being addressed by tanking hotfixes and PTR changes. In the end, however, the great shakedown for the concept of class parity in Wrath will only benefit warriors going into Cataclysm. Even before that, we're seeing course corrections on the PTR that manage to preserve the inherent flavor of warriors, and to my mind, that's an important goal. I don't want my warrior to feel like a death knight or druid or paladin. If I did, I would play that instead.