Political Memes

I never said they were dumb. But it takes a long time of observing and reasoning to get such a result. And yes, archeology shows that between alternating crops and non-use as the early version and the "modern" three-crop-rotation is a four-digit gap.

humans have been unchanged for over 300k years

This is incorrect. All populations are always changing and being selected, even if the overall variation in a population is much larger than the change over time. See https://en.wikipedia.org/wiki/Recent_human_evolution for more details.

The earliest evidence we've found of agriculture is from no more than 15,000 years ago.

The Roman Empire appears to be the earliest evidence we have of formal crop rotation, but that doesn't mean they were the first to do it.

Letting fields lie fallow to replenish the soil was so important to ancient cultures that it's recorded in the Torah as instructions received directly from God.

Leviticus 25:1-7

The Lord said to Moses at Mount Sinai, “Speak to the Israelites and say to them: ‘When you enter the land I am going to give you, the land itself must observe a sabbath to the Lord. For six years sow your fields, and for six years prune your vineyards and gather their crops. But in the seventh year the land is to have a year of sabbath rest, a sabbath to the Lord. Do not sow your fields or prune your vineyards. Do not reap what grows of itself or harvest the grapes of your untended vines. The land is to have a year of rest. Whatever the land yields during the sabbath year will be food for you—for yourself, your male and female servants, and the hired worker and temporary resident who live among you, as well as for your livestock and the wild animals in your land. Whatever the land produces may be eaten...

You know, like the agrarian peoples worldwide who all independently figured this out almost immediately after starting agriculture....

They're saying no farmers could have figured this out, because only farmers could...