It sounds like you agree with that book on pantheism. But I think this monistic line of argument against dualism comes down more to a semantic distinction than to a discovery about the nature of the self. You concede there's a "sense of self" that wrongly deems the "self" separate, or that there's a "self-belief" that attempts to satisfy its needs, which causes suffering. But that's to concede dualism via the "illusion" of separation from nature. You call it a misleading illusion, while the dualist calls it an emergent property. The difference between them is normative, meaning that you don't like the separation and would prefer everyone to think differently to end our unnecessary suffering. Nevertheless, the separation is real enough as this "illusion"/emergent property that impacts our social and individual behaviour.

Illusions are real, in that they really happen. So it's the "unity" of nature that gave us that illusion and that divides itself through us, just like it effectively divides itself into solar systems or galaxies, or into what's inside or outside a black hole. Orders of being emerge in nature. Personhood evolved from animality, and life from nonlife. Those divisions aren't misleading, although you can emphasize the continuity or the discontinuity between the stages or levels. Again, that's a normative question that comes out in semantics.