The same is true of greek gods. Some of them, like Zeus, were probably real people that existed a long time ago
This all to say that the word (and the sacred culture attendant) is far older and far broader than can be ascribed to some just-so story of a prehistoric, let alone proto-Greek, warlord. If I were to look for origins of “Zeus,” the god, I would instead first contemplate how vast the sky appears when seen from the steppe (whence the Yamnaya, first speakers of this language family). How does one not imagine a sky father in that seeming infinity?
The story of who a person was can easily be a combination of many.