> As auto-generated it can support more features than even an advanced generics could provide.

No, it can't. There are patterns that no monomorphization strategy (including code generation) can express. For example:

    func MakeList<T>(x T) List<T> {
        ...
    }

    func Foo<T>(x T) {
        if ... {
            Foo(MakeList(x))
        }
    }

This is a contrived example, but this shows up from time to time in functional data structures.