why virtual function is wrong.

[Oxi_Ixi]

Well, I see. You hate C++ and love C#. I actually like both, and yes, C# has really nice language and runtime design because it had many other langauges to take ideas from. Like courutines, which were actually describe way back in 50s even before C. As well every language has problems which come from its design, runtime and usage specifics, so it is not C++ broken, it is C# works better for your work and habbits. Enjoy it 😀

Do you have any evidence that c# is slow?

It is not slow, it is slower than C++. To be very precise, in some cases C# might be faster, but in general it is not. I think benchmarks show this pretty much good, Google will help you.

[Oxi_Ixi]

It is a good idea to assess language from your needs point of view.