Can we be certain whether it was drawn in a simulator? It has several markings and notations which suggest it was done in a drawing program for electronics.
In any case a simulator is able to calculate for 3 transistors/ mosfets the same way it does for one transistor. It may take longer to run since it is more complicated. And it's easy to make mistakes when drawing it, causing more errors. These have to be identified and corrected. And there are times you need to use a handy trick so the simulator doesn't hang.