To summarize, Michael Vassar offers Bison on the Great Plains as evidence that maybe farming was not clearly superior to hunting (and gathering) in the number of humans a given piece of land could support. Well, here is a quote on the Bision issue:

The storied Plains Indian nomadic culture and economy didn’t emerge until the middle of the eighteenth century. Until they acquired powerful means to exploit their environment—specifically the horse, gun, and steel knife—Indians on the plains were sparsely populated, a few bands of agrarians hovering on the margins of subsistence. Their primary foods were maize, squash, and beans.

Hunting bison on foot was a sorry proposition and incidental to crops. It couldn’t support a substantial population.

Source