Turns out, while I have a bit more recent hardware, I'm affected by this problem as well. The whole game stutters visibly and frame rates drop very low the more units exist.
I'm using a AMD GPU with Wayland on Linux. It doesn't matter whether I run the game with Wayland or XWayland. It doesn't matter whether I select OpenGL or Vulkan as engine. It doesn't matter whether I enable GPU Skinning or not and the problem continues to exist even on lowest graphics settings.
What seems to be common from the reports so far is that a lot of time is spent in "sim update", but I'm not sure if that's significant.