Yeah, at the time of MoP it felt like they could have done something with that theory, but then everything after MoP has undermined the whole concept by showing the Alliance and Horde to both be consistently weak and inept whether they’re fighting each other or not.
Even Chronicle’s whole thing about the Old Gods seeing that the strength of a united Alliance and Horde would be unstoppable was outright discredited when Legion started with both factions crashing and burning in the first engagement so badly that they were practically forced out of the war altogether.