I listened to parts of the video, and I'd like to address a few points. You mention that Taran Zhu should only care that the excavation was Garrosh, and not the entirety of the horde if it was part of the start of the rebellion. The rebellion started BEFORE the excavation, which makes the distinction between who's digging and who's not even more important.
Also, while the Shrine is completely open, and they may be able to murder Horde members in their sleep, do you think it would end well for them? Taran Zhu got choked out by Shan Bu, and would have died there if we weren't there to single-handedly save him. I say single handed, because the Pandarian NPC that tags along really doesn't do anything. You can argue mechanics vs lore there, but you cannot argue that Taran would have lived through that without our help. He was begging us to kill Shan Bu as he was being manhandled.
You keep bringing how how awesome the Shado-pan are for defeating a band of Zandalari trolls. We saved, in lore and in game mechanics the Zandalari trolls from the Gurubashi and their god. We also defeated the Amani and their gods who were more powerful than the Gurubashi who were more powerful than the Zandalari. So the Shado-pan manage to kill the remnants of a broken tribe, after all of their great warriors and priests fell to internal conflict, battles with other tribes, and trying to stop the Gurubashi? And this makes them look like bad mofos? They slaughtered the desperate leftovers looking for a new home. I'm not saying that the trolls introduced themselves in a nice or pleasant way. I'm saying the Shado-pan were not dealing with what could in any way be reasonably described as a formidable military presence. I don't have time to research this, but from what I remember the Zandalari are practically the librarians of the trolls.
As far as the mantid, when you finish the Klaxxi quest, he basically tells you all the Pandas have been doing is culling their weak. I doubt that it was going to end well for the Pandas when the mantid actually attacked them.
Is Taran Zhu right to be angry at Garrosh? Sure. If he acted against Garrosh, or either faction, would he be crushed into furry paste? Absolutely.