I’m not so far into this that I think flying is a WoW killer, as much as I wish it was. But I can’t be convinced that flying does not harm player interaction. I have so much more fun when I actually can see people doing things, maybe help them with mobs/PvP, make a friend for a quest, ect. None of that happens in the later part of the xpacs when flying gets enabled.
Not to mention how flying removes strategy from the game, you can’t create choke points or be a road bandit, no epic wars over NPCs, no fighting over resource nodes, all that.