That's a conceptual argument, not a mechanical one, and it's the mechanics that cause the issue. More to the point, it's not really a conceptual argument that addresses the issue. Firstly, religion as a concept is a development - but only to a limited degree (the extent to which settling large communities and developing the ability to build places of worship) is it a scientific rather than social development. So if we're modelling scientific and cultural advances on different trees, that doesn't argue for putting religion on the 'science tree'. Secondly, the way religion is implemented in Civ V and Civ VI - unlike Civ IV - there is a difference between religion (=the faith resource) and specific religious systems. You don't rush to research Confucianism. Presumably faith generation is still going to be linked fundamentally to districts and buildings that are unlocked by technological progression, as is the culture generation that allows you to progress on the social tree. I'm reserving judgment on the way the map will impact strategy at this point. From what I've seen it looks as though most tech boosts are linked to things that are only peripherally dependent on the map (you can build 3 farms or a district anywhere, or make contact with another civ on any map) and seem designed to be 'gameable' to the extent that you're told in advance which actions will always contribute to which advance. Aside from fiddling a bit with which buildings etc. care about which terrain (which happens with every Civ game), this seems to be the main way in which the map is intended to influence how games play (beyond the way it always does in Civ games).