Now in Pandaria, we see the end result of that. One side had to go evil to make the war "fit" with modern sensibilities. Thus one of Garrosh or Varian had to go bad, and Garrosh was the one chosen.
That sets up two stories: a civil war within the Horde, and the Alliance attempts to finish Garrosh. Of those two stories, the civil war is always going to be the more interesting story.
There's a nice cutscene, though:
The writers' work with Jaina has been the major standout this expansion. They've done an excellent job with her all around.
I wasn't really on-board with all the "Garrosh 2.0" complaints about the storyline earlier. But it's looking more and more like this expansion will be a re-tread of the Pandaria story line. There's some differences, notably Sylvanas is treating the rest of the Horde much better. But her character and motivations are really mysterious. There's been no attempt to get Horde players to sympathise with her or her aims, even if you disagree. That lack makes it really seem like they're setting her up to be deposed.
Oh well, there's still plenty of time left in the story. Perhaps Blizzard will surprise us.
I think this story illustrates the disadvantages of "going big". If Sylvanas hadn't burned down Darnassus, there's actually a lot more room for the story to manoeuvre. But because she did, the story points in one direction. Though imagine a scenario where Sylvanas sues for a peace or truce that leaves her as Warchief still. Anduin agrees to this truce (as his nature inclines him to), and that causes a schism in the Alliance as the Night Elves, Worgen, and Kul Tirans strongly disagree. That would be an interesting turn of events, and move the "civil war" over to the Alliance side.