The amount of ignorance in your post is astonishing. Growth slowed in WotLK because of what's called market saturation.
Flying did not kill world pvp, and I can tell you this because I actually PvPed exclusively in the entire expansion.
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The bolded part can be applied to Classic. And no, it's not watered down at all. Lol. It's mechanically Vanilla but with more stuff, new stats, gems and so on.