Your self-sufficiency still depends on reasonable weather. If it's too wet or too dry or too stormy or too sunny, your crops fail and you starve.
The most useful thing civilisation does is manage storage and distribution of food to create a surplus and a safety net. (For most of the world.) The second most useful thing is management of infrastructure, including irrigation, drinking water, drainage and power distribution. The third is centralised access to expert services, including R&D/innovation, and medical care.
If everyone is a smallholder, all of those become more complicated and potentially less effective.
