That seems a bit harsh judgement for a game with a German name, made by 4 German game design students living in Berlin, with funds from the German state [0].
That was one thing it seemed to simulate pretty well in my experience. Last time I played it, I set up the city with a bunch of low income housing areas in industrial zones, roads all through them, small housing plots next to industry and under overpasses and stuff.
The neighbourhoods looked exactly like the low income housing neighbourhoods around industrial areas I've seen in real life. The people in those houses were typically unhealthier than in other areas. I put the closest hospitals and schools just outside those areas, the waste water from the city was dumped nearby etc.
It's quite possible to create extremely disparate neighborhoods and areas. From slums to McMansion filled suburbs to bustling industrial areas.
Sadly though, my in game city started with me trying to model my real city. It turned out pretty accurate at least as far as neighbourhood layout and visual income disparity went.
In contrast: creating Slums in Ceasar, Pharaoh, or Tropico is an explicit strategy. Why? Because low-income industries (such as mining or farming) cannot afford better housing. The slum is the best that you can give that population as a leader.
In Ceasar, they're extremely cheeky about the highest class of citizens. Only plebeians work. If you "upgrade" housing to the point of attracting patricians, you LOSE workers (because patricians don't work!!). There are entire strategies in the game about attracting as many plebeians (working-class) citizens needed to have a functioning economy, but then converting the excess workers into Patricians for higher-tax collection.
As such, you need to keep the plebeians purposefully at a lower class to keep your industrial sector working. If you convert everyone into patricians, no work would get done at all. Its a challenge to build road-networks that separate the housing units, but provide the workers needed to serve the upper class (ex: services such as bath-houses and marketplaces are run by plebeians, but should be placed inside of Patrician neighborhoods)
Ceasar, Pharoh and Tropico are actual games with goals, win conditions and a point.
I didn't like Cities mostly because nothing you did mattered. Not just slums or anything else. You can kill off half the city by accidently routing waste dumping to the city's drinking water and within 15-20 minutes your city's back to being fully populated.
Trying to play Cities strategically the way you would those other games is going to be disappointing no matter how you build the city. It's just not that kind of game.
There might be seven or eight levels of "common" housing that provides workers and then two or three of "upper class" housing that doesn't. But at least to me, a block of insulae isn't a "slum" in the game--a couple of huts with no water or food are.
Sim City btw, does the same thing with Residential / Commercial / Industrial zones. All "traffic" start from a residential zone, then goes to a industrial zone, and finally ends in commercial.
That means a singular tile of "Residential" zone can "feed" the entire industrial sector. While a singular "Commercial" tile can serve as where the industry drops off their goods.
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So I knew that fact for Sim City (and took advantage of it in some designs). I never really knew that for Caesar / Pharaoh.
Also the annoying Western/Eurocentrism.
Eg: See the recent game Dorfromantik, its aesthetically pleasing, it is rustic european scenery, but why isn't it not set in Indonesia or Ecuador or Uzbekistan?