I would say that it is. While WoD certainly has some flaws, it's still better than MoP was pre-Thunder. And it's certainly a hell of a lot better than WotLK was pre-Ulduar (hello, revamped facerollable Naxx!). And everyone seems to hate how Cata was on release, and cried endlessly about the dungeons being too hard.
The only expansion that people didn't whine endlessly about during the first half of its lifetime was TBC. But that's hard to compete with now, as vanilla had a lot of obvious flaws that needed fixing, like the completely screwed up talent trees, the ultra-obscure libram system, and the extremely boring vanilla healing model.