Yeah, I concede that it absolutely is a lot of hand-waving. But we're also talking about emergent properties: it's possible to understand why they arise, what the emergent properties are, and how the underlying system works, without having full information about it all. In fact that's a very analogous situation to our thermodynamic understanding of gases, or fluid dynamics.

I don't want to mislead, there is an incredible amount of stuff we don't know... But we do understand more than most well-informed people think, even people in adjacent fields.