(AVI Update: I asked Jonathan to write about this because it illuminates real-world behavior. And then Instapundit quoting me about Thomas Ball come up, to give evidence for Jonathan's point.)
It's true, they were very overpowered. But if you ask them, they'd deny it. There's a feeling of persecution in certain online communities. As an avid gamer who plays World of Warcraft*, it used to amaze me when people felt like the game developers were persecuting them specifically. However, it's happened enough that I'm now certain it's related to innate human failings. I've found a few recurring themes that tie into meatspace behavior as well.
Once you give people something (i.e. a new spell that inadvertantly makes them the most powerful players in the game), they resent forever when it's taken away. Even though what they were given was unfair to everyone else in the game, they still view it as their "rightful" place. Three years later, they are still complaining about how their healing throughput in raids has gone down from Burning Crusade, and that Ghostcrawler loves hitting paladins with the nerfbat. For real world examples, see every border dispute ever.
People cannot believe that their group ("class") is weaker than any other except for nefarious purposes. So if they are weaker than others, it's because the game developers HATE THEM and have no conception of how their class works. It couldn't be because of a flaw that just needs to be tweaked, it must be because no developer in the entire company plays a warlock and just doesn't get it. Real world example- every teenager everywhere complaining about their parents, and every moron who believes the government is organized, evil, and secretive enough to carry on plots to take down towers, import crack into neighborhoods, etc.
These are often very bright people, but they can't see through the obvious inadequacy of this viewpoint. And they have a target. They become convinced that the lead developer for World of Warcraft, Greg "Ghostcrawler" Street personally despises their class and that's why they are no longer the best class in the game. Or that Activision, the parent company that owns World of Warcraft, is somehow profiting by making their spells weaker.
I shake my head in amazement at how stupid they are, then go to work and complain to my co-workers that the pension team just doesn't understand how important the health benefits department is, and how they just can't grasp how our work is more important than theirs.
*check the author, this is not AVI, who was so offended by Tauren Paladins that any hope of him playing WoW was lost forever.