I don't think that it is a mandatory requirement to have cities in a 4x strategy game. What is your world scale? Is it a world with armies and supply convoys and fortifications? Or is it a scale of villages, groups and barricades?
I like the total war games with their epic scope and thousands of units per army. You can sometimes feel you are like a general commanding an army! But I don't feel the same way about this game.
In all of the examples that are given in your photos we have the bizzare visualisation that a few units are representing something much much bigger and it just looks "wrong", to me at least. I do like all of the games that you have posted images of and I have played most of them...but the city sieges in this game do not have to be the same.
One example that you did not show is in the Disciples games where the city is defended by a massive single unit (rather like a titan) that can only be overcome by a highly upgraded and numerically stronger force. The main locations are almost impossible to take by siege. It is a different approach but not necessarily a better one.
I think the idea of a "city" is a bad one in a game with the scale of the units used here. I can see the city as a backdrop or a staging point in an RPG sense.
Now the idea of a 4x without cities to conquer may seem rather usual but it is about scale. A village could be a strategic location.
I wonder if you have seen Akira Kurosawa's film, "The Seven Samurai"? I highly recommend it. This film shows how a small group of highly trained samurai warriors defend a village using excellent strategy. We may end up talking about the difference between strategy and tactics...