[petrocrat]

The over simplification here is that not all plants are equal and not all soils and/or climes can support all plants. So for soils or climes that can only really grow "weeds" that are inedible to humans, if you put them through an animal (specifically a ruminant), then it converts biomass that is inedible to edible for humans.

The effect of this on your diagrams is in diagram 2, with the intermediate farm animal, there are many situations in that scenario where the calories from those plants would be entirely lost, not simply rerouted losslessly to human consumption.

[hx8]

This is such small portion of all meat on the market, it really shouldn't factor into the discussion for how to feed a population.

[hollerith]

You know this how? Have you done a calculation?

It seems to me that there are many grassy hills that cannot be farmed using tractors and to farm them using hand tools is too labor-intensive.

[hx8]

That's a great question. It's actually hard to get this type of data. I once tried to calculate something adjacent by looking at feedstock production, but actually a lot of feedstock is used for 'biofuel'.

My knowledge comes from exposure to the agricultural industry. You might be able to find some animals grazing on a grassy hill, but that doesn't scale. In addition, most NA climates don't support year long grazing.