WoW will benefit from healthy competition and we are already seeing the benefits with sooner-than-later QOL for customers, an interview detailing future accessibility as a focus and more and more requested changes being implemented.
They need to be scared. That's capitalism! People think there can "only be one" big MMO and I disagree, both will likely continue on and respond to one another.
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If a western game designer told people to play another game while they work on updates they would be crucified. Completely different culture, in America its a huge sign of weakness that people would prey on like animals. Hence why very very few game developers apologize ever, and if they do they its often because have nothing to lose (indie studios).