So how would you solve the AOT (ahead of time compiling) problem without code generation? An entire ecosystem (Unity) that uses C# requires that code must be AOT for supporting IL2CPP (a low level translation of IL to c++). Dynamics and Reflection of non-AOT types are unavailable at runtime. IL2CPP came from Apples requirement that no JIT be run in apps and to get more performance; especially, for features like burst that allows writing C# that directly translates to high performance multithreaded c++.
Different usage, I think: if people are talking about "language not expressive enough", they're referring to mechanisms for generating C#, or IL, not things further down the toolchain for AOT.
System.Xml.Serialization, for example, relies on generating assemblies at runtime to work. That's "code generation", but of a kind that directly conflicts with the AOT meaning of "code generation".
