C# is used by hundreds if not thousands of games by ways of Unity and is therefore demonstrably good enough in this scenario. Furthermore, just because a language is not C++ does not mean you shouldn't take every opportunity to give programmers tools to write fast code - at the end of the day I doubt anyone would be interested in a language that is purposefully slow.
Performance was a core feature of the language (yes, yes, it's managed) from day 1 with unsafe - it's nice to see further improvements in that department.
Use C++ when you need to, definitely, but when you're copying about 256 bytes around for a trivial world-view-projection matrix multiplication[1] you have a problem.
[1]: https://github.com/dotnet/roslyn/issues/10378#issuecomment-2...