Ah, but you see he didn't write operating an MMO, he said "Game design".
Absolutely true. The day-to-day operations of running an MMO (i.e., keeping the servers up, fixing bugs that crash the client, etc.) are totally their responsibility and should be acted upon. However, for example, demanding that Tanks should have more threat generation capabilities, is a
Game Design decision. A decision that needs to be weighed against factors
other than individual opinion or personal observation. This is where you trust Blizzard as a company to do their due diligence, listen to the feedback, take in all of those factors, and produce a change/fix/or
no change to continue to make the game "fun" and continue to keep you paying.