Brooks made that battle work by having the military be too dumb to set up a simple stone wall 8 feet high in front of the advancing zombies. Or if there was no time for stone, city busses lined up nose-to-tail.
There were a million zombies. A stone wall or couple buses wasn't going to stop them. Just look at stuff like this
Brooks does discuss instances where those tactics worked (the ancient Romans) and when they failed (the French Foreign Legion) in The Zombie Survival Guide.