It doesn’t need to be one person. Even 1 thousand people who have everything they need from vast swaths of land and automated machinery need nothing from the rest of the billions. There’s no inherent need for others to buy if they offer nothing to the 1000 owners
Then we are back to individual kingdoms and hordes of unwashed masses sloshing between them in search of easy pickings. The owners might not need their work, but the masses will need to eat. I think sometimes people forget how much of a delicate balance current civilization depends on.
