I don't think that's true, and I don't think the juice would be worth the squeeze. Unreal's flavour of C++ is heavily managed, relying on preprocessing of header files to create garbage collecting pointers and a whole heap of other things you don't think you're signing up for when you think about a C++ codebase. There is no simple place to begin if you're trying to make it C# friendly.

But most of my issues have been with engine philosophy, where Unreal has bent over backwards to expose things to their visual scripting language. It feels like every single feature has a mandate to work in a blueprint tech demo, and as a result few of them are pleasant to code against and almost none of them work together coherently. These are not issues that depend on the language used.