At Wrathgate, technically, our characters are not at the battlefield . They're overlooking the battlefield from their perch. Yes we're there, but the POV of the movies is not our characters. It is a separate cut scene.
Yes, but they still see what happens at Wrathgate. I mean maybe Tirion asks us to leave when the fight is over, but unless that happens I'm not sure why our characters wouldn't stick around to see what happens afterward, knowing what was told to them in the Halls of Reflection. Most of our characters strike me as the kind that like to make sure things get done.
When Tirion speaks, people believe him. You can speculate, of course, that it is Bolvar, but that would mean you don't believe him.
It is just as plausible that the Scourge are going to war against themselves, ala the Zerg after the death of the Overmind. That powerful Deathknights and Banshee's and Vyrkul are warlords vying for control.
Well yes, I'm not arguing that part. I just disagree that our characters aren't there when it happens.