Brother, I see the point you're making with the three-men-on-an-island example, but I think it actually supports rather than undermines the tribal view.

In reality, those three men would almost certainly die fairly quickly. As soon as any one of them is unable to provide food for himself for even a couple of weeks (injury, illness, bad luck hunting/gathering), he is at a massive disadvantage. In a tropical environment where food might seem plentiful, infections run rampant; the first time one cuts his foot badly, he will likely die of infection without group support for care, sharing, or protection.

Individuals on their own die alone and have no reproductive future. As a result, they actively seek out people of like mind or values and join forces with them, or they adapt their values and behaviors to fit the tribe in order to survive. For roughly four hundred thousand years of human history, shunning or exile was effectively a death sentence.

This doesn't deny that individuals are unequal or that they bring different strengths and weaknesses. Quite the opposite: it is precisely because people are unequal that they form tribes, allying with others who complement their weaknesses and amplify their strengths in the face of a harsh world.

Think of individuals as sub-atomic particles. They exist, they have unique properties, and they can interact; but they are far too unstable and vulnerable on their own to form the basic building blocks of a functioning, long-term society. The tribe is the atom; the smallest stable unit that can actually survive, reproduce, and compete in the real world. The tribe isn't just a "molecule" that emerges optionally from individuals; it has been the essential survival unit for our species across almost our entire evolutionary history.

In your example, the three men on the island would die.

As soon as any one of them is unable to provide food for themselves for a couple weeks, they will be at a huge disadvantage.

In a tropical environment, where food is plentiful and easy to get, infections run rampant. The first time one of your three guys cuts their foot, they will die of infection.

Individuals on their own die alone and with no reproductive future. As a result, they find people of like mind or values and join forces with them OR they adapt their values to suit the tribe to survive.

For about four hundred thousand years shunning or exile lead directly to death.