Previous civ games have always had something to limit super expansion. Civ5 had global happiness. Civ4 had a city maintenance cost based on distance from capital. Civ6 does not really do anything meaningful to slow down warmongers from simply expanding into a super big wide empire. As a result, it is too easy to just keep expanding and expanding. Now, I love wide empires but I think there needs to be some push back mechanic in the game so that it is not so easy. Amenities are not enough to slow you down because there are plenty of ways to get amenities in the game. And besides, a lack of amenities might hurt your cities' growth but it does not really stop you from getting more cities. I can have a super wide empire and my cities might be "displeased" but it does not really matter because with that many cities, I still come out way ahead in science, culture and production. I would propose adding a negative loyalty modifier to cities based on distance from capital. The way it would work is the further away cities are from your capital the bigger the negative loyalty per turn. This would force the player going super wide to focus on loyalty if they wanted to keep the far away cities. And there might be some distance that is so far that even with loyalty boosts, you would still lose the city and thus there would be a soft limit to how far you could expand.