The wildlings aren't exactly a disciplined army. Even if Mance was a great tactician, it's not as if the different groups would all do as he says outside of the most basic commands. I thought the fire was supposed to be used as the signal for the raiding group south of the wall, but there are some inconsistencies there... even if the warg is killed, they'd still be able to hear the start of the battle.


The backdrop of all of this is that the wildlings are really only at the wall because they're running from the white walkers, not because they decided to make a concerted effort to invade and plunder. Many of the 100,000 aren't fighters since whole families etc. are there, and of the fighters I'd expect most of them to be self-serving. We're seeing the attack from Jon's point of view, but things should look pretty desperate from the wildling's point of view as well.