Which neatly raises the point of how modern large monoculture does a lot less of that kind of use of agricultural products unusuable by humans.

Absolutelly, the whole of a cow slaughtered in a slaughterhouse is famously used (down to the hoves) and nothing thrown out, however you don't see goats being raised on the unusable parts of a corn plant (whilst wheat straw is actually used as feed, for corn the silage for cattle made from it uses the whole plant including kernels not just the left-over unusable by humans parts).