My first few? I still have the same chartacer that I had in the beginning. To the point of the post, the characters in Degrees of Lewdity are all very simple two-dimensional archetypes, but they fulfill a function within the narrative of the world. They are part of a living story. The same cannot be said for the complete non-charcaters that populate Free Cities. There is no Robyn to feel obligated to in Free Cities. There is no Kylar who requires that you endure certain hardships in order to reap useful benefits. There is no Black Wolf, who allows you to briefly play at being wild and free even though you will always be tethered to the reality of the game's world. There are no characters at all in Free Cities and no narrative that you are allowed to integrate your played character into. The world follows no coherent logic and makes no demands of the player. You can't craft a story in Free Cities the way that you can craft one in Degrees of Lewdity. Free Cities is just a vapid power fantasy where only one character (you) matters, and that is something that I find to be too disaffecting to ever feel dark. It doesn't help that the devs wasted years making giant robots and space lazors instead of world-building.
I think you might be mistaking a game's thematic tone with a game type. While both these game are html-based, FC is a flawed pornified economic simulator, while DoL is a pornified adventure game. While it is tempting to treat highly customizable slave paperdolls in Free Cities as NPCs, the are in fact just your units serving a weird economic purpose. Your role as the PC is to run an archology by making shitloads of money and gaining reputation. Most of ways to earn money and reputation are through sex work of varying kinds. That's it. At some point the overload of micromanagement in this game becomes unbearable and you simply loose interest in your army of buttsluts, submissives, masochists, blowjob artists, humiliation sluts, human cows and broodmothers with their extensive wardrobes, body implants and crooked teeth. You would similarly loose interest in playing Civilization franchise if you had to spend 3/4 of your playtime naming and renaming your units, adding this or that type of ordnance they carry and most of that would be presented as walls of hyperlinked text and unending collapsible end-of-turn reports. FreeCities would be much more fun to play if it utilized a Theme Park style of engine, for example.
Having said that, we are talking about a sadistic game at heart, where humans and human sexual interactions are broken down into configurable sets of parts and stats, to a degree rarely seen in other games. And sex is directly converted into money and influence, there is no other use for it. And to make it darker, as others mentioned, there is no higher purpose in whatever you, as the player, will do. You can be a psychopathic bastard, maiming and killing your slaves at a whim, or you can be a protective, breeding Daddy - doesn't really matter, as long as your balance sheet is ok.
You don't have much of that in DoL. Yes, ultimately the game is a neverending story with no particular goal other than paying your (easily avoidable) weekly rent. But it is not as nihilistic as FC nor extreme in the dark sex content available.