Problem is Wow isn't known for world pvp either.. its either too laggy or completely unbalanced.. as you stated there are always ways to avoid it with stealth and trying to evade the servers/client can no longer handle the number of dice rolled by rng, so world pvp will never return to wow as we stand, so why ditch flying to try to help a dead system?
plus as said many servers aren't pvp now with warmode also.. all servers are pve so pvp combat being part of the world is a very small part.
There is zero reason wow can't be a massive game with a lot of areas you can explore with a flying mount just like Northrend.. fly around northrend and find the lil areas you've never found before stormheim is a great zone for that, and Icecrown because of the SCALE of the buildings you feel small even in the air, there are more than enough tricks to make flying feel less like taking away from the world just that wow Dev's haven't been allowed to make games for fun anymore.