It is not just monoculture that has created this increase in production. It is also increased inputs like fertilizer and pesticides. At a certain point the pest

It is not just monoculture that has created this increase in production. It is also increased inputs like fertilizer and pesticides. At a certain point the pesticides stop being effective and the ground needs so much fertilizer it increases prices. This happens on hundred year time scales, so you can't just look at a small portion of ecological history to reach conclusions. You are welcome to think what you want, but everything I have read about agricultural ecology suggests that nature is stronger than our science. Pests evolve (perhaps slowly, but faster than the science we stole from nature). Naturally enriched soil is more fertile.