I think part of the complaint has less to do with language toolchains/extensions and more that the post processing performed on the C# output via Binaryen is not unique to the toolchain. It's analogous to comparing the toolchain outputs while zipping one output but not the other.

I think it's also a bit unclear exactly what you mean when you list nonstandard C extensions alongside Rust's no_std and then say "similar approaches". Rust's no_std is part of the language proper so the commonality surely can't be the non-standard-ness of what is done to shrink binary sizes.