It involves a lot of zone switching and questline micromanagement, while speed leveling helpers such as Azeroth Auto Pilot are specifically designed to limit the amount of jumping around players are required to do.
That said, while this newer route is slightly faster and doesn't have nearly as many players following it, it does have a few downsides. Update: Timing is everything, as DesMephisto just beat this time on stream using a similar, though slightly more involved route in 5 hours and 35 minutes, showing that there's still room for optimization and competition in speed leveling! Harldan's Reddit post goes over the route, but there's also a video guide as well as a recording of the full 5h 44m speed run, which also covers all the gear and consumables used along the way. A new speed leveling route has been discovered, taking Horde players from level 10 to 50 in just 5 hours and 44 minutes! Harldan came up with the route after feeling that the recently nerfed Warlords of Draenor content featured in Azeroth Auto Pilot routes had begun to feel sluggish, and although the new route still makes extensive use of WoD content, it replaces the slower questing areas with Eastern Kingdoms and Kalimdor zones, making it about 40 minutes faster than the previous route.