I often see things like “Ancient Egyptians believed…” and same for Ancient Greeks or other civilizations. Did essentially every ordinary person in these civilizations really adhere to the same religious/belief system?
It would be crazy to say “Twenty-first century Americans believe you go to heaven after death,” without further specifying the demographic. Are we exceptionally more diverse than cultures were in the past?
I discuss this question a bit in this answer on the Tiwanaku culture in Bolivia and Peru. Essentially, there is a very clearly identifiable Tiwanaku state/elite religion with an emphasis on large-scale communal practices, a particular set of psychotropic rituals, and a distinct visual style. The extent to which these filtered down into everyday practice, however, varies between regions, cities, and even between different neighbors in Tiwanaku itself.