Pastoralism is brain rot, we should not romanticize "small farms". The romanticization of farming probably has a lot to do with bad agricultural policy. (In the US we can blame the senate, but what about in Europe?)
Also, are there any agricultural billionaires? I kind of doubt it: usually they are rich but not that rich.
I don’t know which era you are talking about. I was talking about the decade after 1989, about when the Soviets were collapsing, before the recent economic downturn. They were not importing food, nor were there oil available to run trucks, tractors or make fertilizer - https://www.architectural-review.com/essays/cubas-urban-farm...
Cubans were literally starving and caloric intake is estimate to have been reduced by 38% in the period you are talking about before food imports resurged. [0]
Another great example case, thank you for pointing that out.
Show how the productivity per acre of arable land times the amount of land available produces enough calories to keep the current population of the world from starting. If you can't produce enough calories, vitamin content doesn't matter.
(hint: the productivity of small-scale farming is often << 10% of the productivity of large-scale farming and the productivity of garden-scale farming is typically < 1%)
Those are some overly broad assumptions with using calories. Not all calories are the same — some foods take more calories to digest, and others, like MCT takes very little to get absorbed by cells. It really depends upon the food being consumed.
Nutritionally-dense food can also change gut biome. I have no idea if anyone ever did a study on long term effects, but it would be interesting to see if the body ends up needing less overall calories if the food quality went up, along with changes in the gut biome.
As far as productivity goes, I don’t think the figures you are quoting takes into account methods other than monocropping. Industrial scale famers who went to polycropping, for example, find smaller yields on individual crops but their overall yield and profit were better. No-till, as another example, underperforms until about five years in.
And then there are losses during transport.
The closest I have seen was someone attempting 100% of his diet from gardens he has planted for a year or harvested himself. It was rough, in a tropical climate (Florida), but was possible. He had to use three gardens, though the deal he made with the residential landowners gave them the right to harvest anything at anytime in exchange for using their front yard. According to him, 80% was doable. I don’t know if he had integrated livestock.
As I mentioned in other comments, post-Soviet Cuba, under sanctions, were forced into developing this because of the lack of oil (trucks, tractors, fertilizer, and pesticides) and other imports.
Also, are there any agricultural billionaires? I kind of doubt it: usually they are rich but not that rich.