Earlier quoted context omitted.
It's a classic victim of shitty, shitty software developers who blames tools rather than taking ownership. Or shitty software dev companies that push out crap to meet marketing deadlines. Either way, take your money elsewhere.
Given that a number of other Unity-based games have had the same or similar performance issues, including KSP1, the Endless games, and others, it seems the problem is very much that Cities Skylines 2 is hitting up against the performance limits that the Unity engine is capable of without custom modifications to the engine-layer codebase.
The fuck up here is whoever was handling the art assets. You simply do not ship a game with such detailed graphics and no LODs. They must've simply been downloading things off the asset store and throwing them in without any regard for performance.