Why Cities: Skylines 2 performs poorly

Cities: Skylines 2 like its predecessor is made in Unity, which means the game can be decompiled and inspected quite easily using any .NET decompiler. I used JetBrains dotPeek which has a decent Visual Studio -like UI with a large variety of search and analysis options. However static analysis doesn't really tell us anything concrete about the rendering performance of the game. To analyze what's going with rendering I used Renderdoc, an open source graphics debugger which has saved my bacon with some of my previous GPU-y personal projects.

An incredibly detailed look at just what's going on under the hood to make the new Cities: Skylines 2 behave so poorly.