This isn't about the merits of Pathfinder or not, but rather a critique of what flying does and why it doesn't matter.
Flying more than anything is a way of speeding game progress. While this is especially true for leveling it's also true for world content such as your daily quests.
Now Blizzard has talked about how their dislike of flight often stems from the way it trivializes the world itself. Terrain is no longer a barrier, neither is mob density surrounding assassination targets.
So Blizzard has designed a world where you area expected to experience the world as you level, but what about after leveling?
Well at max level you have two main ways of character progression. Open world content and instanced content.
Instanced content would be:
Raids
Instanced PvP
Dungeons - normal, heroic and M+
Islands
Open world content would be:
Gathering
World Quests
Open World PvP
Meanwhile they have created a world where you don't need flight.
No, seriously.
Every single dungeon or raid entrance is accessible almost immediately from a flight path or in the case of many things through a queable system in the menu options.
As are battlegrounds.
The main thing that flight speeds up for people is the open world.
So if you don't spend time in that open world. If you're primarily a raider, M+, PvPer. Then chances are flight isn't really for you and is meant to be a reward for those out experiencing the open world.