The difference is, that in northrend, neither the warchief, nor the high king were present. Thus they appointed field commanders.
But in the broken shore, The Warchief AND the high king are present, thus, they're the ones leading their forces. Not Jaina, not Sylvanas, not Greymane, not Gelbin, not Baine, not Lor'themar.
Vol'jin and Varian.
The VV team.
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Ohh please. I'm gonna eat my hat if he's not dead.
OR rather, its possible he's still alive, but the odds of him going back to being warchief when this expansion is over, are close to none. He's a goner. Either now, or later, but I don't really give him any odds of making it out of this one alive. Feel free to bookmark this post and collect your bets when Legion is over.