It's not really as bad as you suspect. A lot of homesteaders target food self-sufficiency on a quarter acre; while there's some debate [1] over whether that's possible, pessimistic estimates for the amount of space needed to feed a skilled organic gardener's family of 4-6 top out at about an acre. A 100x100m plot is about 2.5 acres.

The bigger problems are a.) skills and b.) labor. Homesteading methods basically require full-time gardening by people who have put significant efforts into maximizing yields, intercropping, planting multiple harvests, growing vertically, etc. The advantage of our mechanized farming system is that we can feed the population with 1.4% of the population.

[1] https://www.theseasonalhomestead.com/the-truth-about-self-su...