It’d be pretty nonsensical to create a new villain in the army of the light, and then just ignore their existance entirely to make up brand new villains out of nowhere for no reason.
Then again, that’s pretty much what Shadowlands is doing so who knows.
Sure, we have the lich king, the void lords, the army of the light, and the horde (maybe) to worry about, as well as the remnants of the legion… but did you know there’s more bad guys in the sky that can only be reached by breaking the lich king’s hat in half!?