I think a lot of the trouble comes from the fact that those two ethics are so closely linked to gameplay mechanics that don't actually exist in the real world. It makes sense for Egalitarianism to be linked with democracy, because that matches our actual experiences, and it makes sense for Militarism to be linked to combat ability, for obvious reasons. But we don't actually have psionics or AI, so it's harder to tell how different ethical camps will deal with them.
It might be interesting to refocus those ethics on some of the new mechanics. Spiritualists already have access to Temples that boost amenities and unity. It would be cool if Materialists had access to a special building that gives them easy access to merchants, something like a reskinned Shrine of Numa (which, weirdly, is very Spiritualist in flavor). If you want to make a lot of money, you'd go Materialist. If you care more about intangible things like happiness and social cohesion, then you'd go Spiritualist.
It might be interesting to refocus those ethics on some of the new mechanics. Spiritualists already have access to Temples that boost amenities and unity. It would be cool if Materialists had access to a special building that gives them easy access to merchants, something like a reskinned Shrine of Numa (which, weirdly, is very Spiritualist in flavor). If you want to make a lot of money, you'd go Materialist. If you care more about intangible things like happiness and social cohesion, then you'd go Spiritualist.