Was searching for this exact topic because I watched a WoD video and ended up finding this thread.
Can’t we all agree that this is a strange writing decision?
We go to an alternate reality and in the past to fight a new Horde brought up by Garrosh - the Iron Horde. So these are ultimately different people, not from our timeline/our past that we’re fighting, minus Garrosh of course.
But, later on in the expansion when Gul’dan summons the Legion to alternate Draenor, it’s apparently the same Archimonde, same Mannoroth, and same Kazzak we’re fighting. And that very same Archimonde decides to send the alternate Gul’dan to our timeline, rather than alternate Azeroth.
That’s a strange writing decision, in particular because this is never stated to be the case in-game. It feels like it was just a writing excuse in order to justify the Legion expansion (which is sorta fair, I can understand that), but that’s still weird. Also, food for thought, do we even know if it’s accurate anymore? Afaik Afrasiabi is the only person from Blizzard to have said this or anything like it, and he’s not around anymore. And, as of Dragonflight, we do see an “alternate” Burning Legion during the Time Rifts shenanigans with Soridormi (alternate timeline where Illidan becomes an overlord over Azeroth).