I understand that the elves have had a bit of a rough ride with humans before, but this conversation would essentially be moot if Anduin Lothar was still alive or had had children as the elves owed allegiance to the Arathi bloodline, quite simply they would never have left the alliance just based on that. Additionally, at the end of the Burning Crusade, it is Velen, not any member of the horde, who restores the sunwell for the Blood Elves, thus halting their slow descent into corruption from using fel energies.

As for the Tauren, camp taurajo was not meant to play out the exact way it did, but beyond that it was not the horde that helped Baine recapture and secure Thunder Bluff after his father's death (at the hands of Garrosh - yeah his weapon was poisoned but regardless it was a duel to the death) it was Jaina, not to mention the connection made between Baine and Anduin Wrynn while the whole scenario transpired. It's hard not to see the horde right now as a weak coalition of semi-willing members, it would not take much at this point in my opinion to really fracture the horde.