It really sort of did though. As soon as you got flying in TBC the world became a complete non-threat, which especially at the time was a major difference. Even areas full of elites that had been extremely threatening and dangerous areas were suddenly "lol, just casually fly right over to the thing you need." It also immediately destroyed any real sense of zone navigation, because even a fairly complex zone to navigate like Blade's Edge got turned into "alt tab while flying in a straight line directly to objective".
I think it's fine to like flying, but also it very, very literally takes the player out of the world. Before it you have a bunch of actual gameplay choices "do I enter this area from the front or is it easier to get to the objective from the side entrance", "Would it be quicker to jump down off of here or is that gonna aggro a bunch of things at the bottom and be a hassle?" "Should I take the long way around or just cut through these mobs and try to avoid getting dismounted?" "There's a herb/minning node up on that cliff/over that little mini canyon... is it worth looping around to get up there/to the other side? Which ore/herb is it?"
When you having flying, all of those gameplay choice moments become "lol doesn't matter, fly straight to the thing". A huge chunk of gameplay does end.
Adding actual flying was a massive mistake. They should have made flying mounts able to jump very high and then glide, either like a lower altitude Aviana's or like the goblin jump-pack things that were sometimes around in BfA. Then at least you'd have to consider approach and how to get around, as well as where you're going to land each time.