I know there are some !Kung who live alright as bushmen, in a mild climate, but it's not an easy life. Anyhow, more power to them if they remove all traces of modernity from their lives.
Logistic map (aka uncontrolled growth of population or overpopulation) is basically the fundamental source of suffering for all living things. Instead of planning for food, nature just overproduces demand and lets the weak starve to death and the average to just starve.
Rather than asking how it would support billions, we should ask how we are planning to not suffer in these numbers. Haven’t heard it regarding our current life style. Everyone tells us to reproduce more and pay more and more astronomic bills and loans, that’s it.
Personally, I would say a lifestyle that isn't just a thought experiment should answer one of
A) How do you support the current population of the planet like this?
B) How do you humanely reduce the population over time if you can't?
The world’s a very big place with a hugely diverse set of possible “valid” lifestyles (and limited ability to influence their reality). So what’s the big deal with proposing that maybe for some people a return to the land or to subsistence is a legitimate option?
A system with free agents is very prone to painting itself into a corner, it’s unstable by design. One of the issues that we have is that on the brink of catastrophe we are still asking ourselves whether the less carastrophic measures are ethical. But times of “we do what we want” end with the last decent square mile allocated for crops and housing.
We’re at such hard physical limits for the first time, so it will take a couple of world wars to figure out new rules, I guess.