I'm under the impression that the Great Dark Beyond is the "space" of the Warcraft universe, while the Twisting Nether is a magic plane between planets, kind of like a hyperspace.
We see that Legion ships warp/jump between places to get there quickly (see; the Kil'jaedan fight in ToS, where the ship is in warp-drive to somewhere), and using the Twisting Nether to teleport would make sense: the Great Dark Beyond and the Twisting Nether are said to be parallels/counterparts made during the Light/Void clash, and while the Dark Beyond is empty and physical in a sense where celestial bodies freely float in accordance with Laws of Physics, the Nether is magical and immaterial in a way so teleporting between places in a literal sea of energy would be cakewalk depending on the size of the vessel (see; Legion ships vs Sargeras' physical body).
https://wowpedia.fandom.com/wiki/Twisting_Nether
https://wowpedia.fandom.com/wiki/Great_Dark_Beyond