Well, the funny part is that for some reason, Sylvanas's loyalists apparently had a bit of the upper hand right before the Mak'gora- Anduin even makes a point of saying they might be the only force capable of opposing N'zoth, somehow. It's supposedly not a SoO situation where Garrosh was backed by nobody but hardline Orcs and goblin mercenaries.
This happening not too long after Nathanos claims the Alliance is weeks away from winning against the entire Horde, and after a war that has been marked by a long succession of disasters for the Horde after Teldrassil. We lost the Undercity, both Warfronts, our War Campaign led absolutely nowhere, and we lost the Battle of Dazar'alor as well, AND had a rebellion. But somehow, after all this a part of the Horde is the match of another part of the Horde plus the Alliance.
Then again, the Alliance was still on a solid war footing right after a cinematic has Genn claim that they're down to sending peasants to the frontlines, so we can just chalk it up to the entire war making no sense whatsoever.