The others help your point but Cities Skylines is memed because it's graphics over substance as it's basically a city painting game with shallow mechanics that most people use to make little city dioramas which is still fun but not deep gameplay.

People mostly complain that it’s not SimCity but the gameplay is fine. It’s in no way shallow. Just different.

It has deeper micromanagement than, say, Planet Coaster, but it is not on the level of gameplay loop micromanagement as the like of SimCity or Roller Coaster Tycoon

The transportation mechanics in Skylines are quite complex and fun. The player can trace individual trips, and some of them matter quite a lot: the businesses need to get and ship their raw materials and finished goods, and the shops need customers.

The budget mechanics are a joke, before long the player has practically endless money.

I'm afraid I must disagree here. I enjoy C:S. But its mechanics are shallow compared to many other titles.

One rather unknown point that, while not directly related, highlights this is how in C:S your income depends on your current budget. I.e. you magically receive less income if you have 10 million in the bank, and receive more if you're in debt. That point alone makes objectively comparing and strategizing unnecessarily hard, and it feels like the game really does not want you to work with numbers instead of paint buckets.

The core of the game clearly is urban planning - properly designing your city to avoid traffic jam and allow the ressource to flow where they need to go - not budgeting. The game doesn't want you to heavily work with numbers because, well, that's not very fun. The budget is mostly there to set the pace.

My issue with the Paradox games is that they have gotten too complicated for their AI, which suuucks. Hearts of Iron's AI has no understanding of its own military strategies, and I don't know how I could have a multiplayer game lasting 80 hours with multiple friends.