Indeed, with polytheism and monotheism, the other gods receded into the background, or were demoted to angels or other lesser spirits.

I agree that this kind of genealogy doesn't logically entail atheism. As you say, it's possible we could be projecting our images onto an inhuman deity that's nevertheless real. But this genealogy does open up a rivalry between explanations. What's the best explanation of this evolution of the idea of God? What kind of deity would be compatible with these tell-tale developments? Is it likely, given this genealogy, that any extant religion's theology is accurate? In short, positing the inhuman, unrepresented deity would amount more to mysticism than to theism, especially as the latter shows up in organized religions.