I feel WoW is so tied to their old 15 year old servers they use, that it cannot be separated unless they make a new game. It would explain why private servers managed to do what Blizzard can't. In fact I think the servers has gotten worse since 2005 :P
By every right in 2020 servers should be able to handle that many people on screen at once, it makes me think Blizzard can't do it, not that they won't.