Please tell me about this gameplay I'm missing out on. Running? Avoiding mobs? Can that really be classified as engaging gameplay? "Should I run through those 5 mobs, or take that path slightly to the left and only pull one? Wow, the decision making is real!". Then you could argue that there is a lot of platforming now. First of all, wow is not well suited for that (Since so many other games do it so much better), and second of all, that platforming quickly runs out since you do it once and then it is done.
So again, give me a single example of good gameplay, that is currently in the game, as a result of not being able to fly. One, single, concrete example, taken from inside the game so that I can go check it out and say "Wow, they are right, if I could fly here, I would be missing out". Because as it stands, it boils down to "I need to get from here to there, and there are 3 elites and 5 regular mobs in the way. I won't be getting anything whatsoever from doing it, and frankly I should just not do it really".