- - - Updated - - -
Choke points do not really have much effect in wow because of the game engine.
1. players can run through each other
2. attacking requires targeting
Even though there are abilities that do not require targeting, they are not really common and are not effective at stopping 40 people from running past.
Alliance could just run through hordes and proceed to kill the boss.
Alliance can't really push into the upper keep until they have a nearby graveyard, since the horde is rezzing right there. Any alliance casualties are taken out of the fight for a long time, spawning back at SH GY or farther north.
Properly executed, and with the usual alliance response, this can lead to the horde zerg beating the broken alliance zerg. No turtle is needed, although one may break out.