80% of the population spent their lives in extreme poverty, toiling in the fields from sunup to sundown.

You can thank the McCormick Reaper for putting that to an end. No need for Roundup.

This common outlook of pre-industrial farming is actually contested, eg. [1]

> One of capitalism's most durable myths is that it has reduced human toil. This myth is typically defended by a comparison of the modern forty-hour week with its seventy- or eighty-hour counterpart in the nineteenth century. The implicit -- but rarely articulated -- assumption is that the eighty-hour standard has prevailed for centuries. The comparison conjures up the dreary life of medieval peasants, toiling steadily from dawn to dusk. We are asked to imagine the journeyman artisan in a cold, damp garret, rising even before the sun, laboring by candlelight late into the night.

These images are backward projections of modern work patterns. And they are false...

[1]https://groups.csail.mit.edu/mac/users/rauch/worktime/hours_...

I had no idea roundup was that old and revolutionary

You can till/plough mechanically destroying the weeds but eroding the soil or you can use Weedkiller instead. But it is hard to use neither and maintain yields.

However it was done, we have much higher productivity requirements nowadays.

Much higher productivity demands for luxury products. If we want back to produce a variety of direct human edible vegetables the productivity would not be necessary at all. When you're raising corn, soybean and wheat for cattle then it's obviously a much bigger higher order problem.

Buckets of free/cheap labor that no longer exists in much of the world.