Well it depends on what you call 'sustainable'. I use a pretty common definition, roughly 'can in this way, without using non-renewable, external energy sources

Well it depends on what you call 'sustainable'. I use a pretty common definition, roughly 'can in this way, without using non-renewable, external energy sources, a population be fed'. If I'm reading you correctly, you're using a definition of 'can this particular plot be sustained as a home garden without external inputs'; well yes, it probably (maybe) can. What my definition adds is 'can the whole population be fed this way'; and no, home-scale agriculture can't do that, in the aggregate (maybe in one village, or a rural(ish) part of a developing country somewhere; I don't care for specific case studies, I'm talking about the aggregate). If some people can feed themselves off their own land, while relying on (many) others in the rest of society to produce stuff and infrastructure etc. who need large-scale agriculture to sustain themselves, I argue that those few aren't being 'sustainable' - just ignorant of their reliance on infrastructure provided by others who produce more efficiently.