My end goal also is not to run 5000 Inhabitants as main course of the game design.

There will be lots of systems, which will affect performance. And things will affect each other.

On second screenshot there are 1000 inhabitants in the area of 100x100m. Which performance wise is much better.

My goal here is to aim above 60FPS. It is good benchmark for me.

And if in the end town will have only few hundreds of inhabitants actively living to keep 60FPS, it is still good.