Kind of ironic that for making a point on C#, you're using F#, an FP language.

I don't see the irony. It's a contrast of a class based and object oriented language vs a functional language. The functional language leads to a much simpler call graph than the OOP language.

The irony is that Go is not a functional programming language.

You're right. One of the reason it has simpler call graphs and less complexity is because it is composition based and struct rather than class based.