The drop in population in historical civilizational collapses are much sharper than even World3 would indicate. World3 assumes perfect allocation of resources, technological investments with no unforeseen effects, no military, war, pandemics, natural disasters, etc.
Also I’d like to add: if the maths behind economic models have yet to be perfected (and are inadequate), we can still look to historical examples as models for collapses from resource shocks. Some good examples include the Late Bronze Age (likely drought), Mayan (drought from warming), Khmer (drought), Ming (drought from cooling), which are all climate/resource related. Food has been the primary energy resource besides wood (which has also led to collapses), but nowadays oil might hold that title. I do think it’s possible that we may get by in a different way, but that’s only because there’s others things we still missed out on our better models (new invention, alien contact, nuclear physics breakthrough, divine intervention, nature of reality revelation, etc.)
Watching Population Bomb (www.resilience.org)