You can't defeat some rogue, fanatic, splinter cell that the rest of the faction not only disowned, but is fighting against, and say you defeated the main body. It would be like a foreign country coming to America and winning against one of those backwards hick militias, and then turning around and saying they defeated America.
But delusional...go ahead and keep ignoring the fact that all the main race leaders of the Horde still exists and are still in control of their people (we could argue about the Orcs, but Thrall is still there), ignore the fact that you defeated (and not without the help of the Horde) a force that is a minuscule fraction of the Horde and the Horde's war might; or the fact that had Varian tried to put restrictions on the Horde...then you would have had an actual war on your hands.