Our models and explanations of the world are dependent on our belief system and the framework through which we look at. For example, a marxist's explanation of the economic system is very different from that of a neo-liberal. The two would not even agree on an ontology, yet alone the mechanism.

Graeber was a self-proclaimed anarachist. His books indeed have a different description of reality than the orthodox description of reality. If you don't agree with his description, then it will indeed look outlandish - the same way an atheist's and religious person's descriptions sound outlandish to each other. If you do agree with his descriptions, or at least that there are many different conceptions of the world, then his views are more reasonable.

Harari is not making scholarly arguments at all, so we cant even say much about his books.