Directly from Lum’s post and following comments:

This just can’t surprise anyone. EVERYONE who commented when Arenas were announced wondered how Blizzard expected them to be balanced, as the classes were NEVER designed for that kind of gameplay.

We aren’t talking about specialized blog comments, I actually remember interviews on mainstream gaming news asking that.

Everyone (including Blizzard) expected Arenas to bring up severe class balance problems. In fact we thought Arenas weren’t the best way to deliver the best rewards as the resulting gameplay wouldn’t be all that fair and balanced.

What people couldn’t expect is Blizzard making Arenas authoritative and compromise the rest of the game.

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I also think Lum is wrong comparing this particular issue to what happened in DAoC.

I don’t remember well the details in that case, but I think it was a change made after a long-standing balance issue. DAoC’s problem was that the original class design wasn’t all that good and laid out, so issues appeared down the road and sometimes they had to redesign a class on the fly in order to actually give it a specific role that it didn’t have. It was a problem of the class and its identity in the game, due to the fact that the game had too many classes and so some “identity disorders”. So they tried to “rethink” the class and consequently pissed off the players.

In WoW the original class design was (arguably) solid and objectively better outlined compared to all other MMOs released. The bigger balance problems arose (and here D-One is right) when the game escalated toward high-end raiding and now Arenas. It was a balance issue induced by mudflation and its pressure on game design. Like the itemization.

It’s as if in DAoC they added a particular keep down the road and then discovered that one class could exploit that keep. And then decided to redesign the class instead of fixing the keep.

WoW’s class design didn’t broke because the original class design was poor, but because they added new gameplay systems (Arenas) that aren’t appropriate and coherent with the original class design. And now, in order to make Arenas balanced, they are producing a chain-effect that has an impact on the class as a whole.