Alliance have a different kind of plot armor.
Now matter how bad they get beat on, now matter how many whipping they take, no matter what stupidity they show on the battlefield, the Alliance is guaranteed to be the winners in the end simply by virtue of being "the good guys"
I would accept that as "fair enough" and go home if it were true. If WE win, not "the players" of either faction win and it's ambiguous who actually killed Garrosh, etc. The Alliance flat out wins the war? fine, but a lot of Horde posters would NOT accept that being the outcome.