also like, i feel civs already had a pretty decent amount of change just from new policies and religion choices? I would have fleshed that out more, using the systems to add more fundamental but still gradual changes to the vibe of a civilization.

Like imagine if there was more interplay between tech/policies/religion so e.g. certain milestone techs or just unlocking enough of them in a short time caused a "societal revolution" that lets you make some juicy changes to religion/policy. You unlock/use the atom bomb and get a choice to pick how your civilization should respond to this new concept: maybe you embrace anti-proliferation which makes both you and anyone attacking you take a hit to happiness for using nukes, or you learn to stop worrying and love the bomb which just straight up gives you passive happiness for every nuke you posses and using them makes your people squeal with delight.