the way it was put out there thats how it came off. he kept saying shyt like "u cant stop them, we cant stop them, and all the southron kings cant stop them, but together maybe we can give those fukkers a fight"
im pretty sure after seeing what happened at hardhome, he would have augmented his garrison with a few thousand wildlings.
his wildling plan had 2 missions. reinforce his tiny nights watch force, and have less bodies for the others to raise from the dead. if the nights king n them get right past him and the tiny ass watch at the wall, he just put 5,000 extra bodies in the north for the nights kind to raise up. just bad move all around if he doesnt post some wildling warriors at the wall.