Fly to Ruuan Weald, then go down the ramp until Gruul in Blade's Edge. You can travel to Cosmowrench from WOW Classic TBC Gold Netherstorm. I'm not sure. I feel that if there were no flying mounts flying paths, these would become important again and fill the gap. If Blizzard developed WoW today the game wouldn't even be called WoW. It's most likely to be an Overwatch MMO, or something...