How so? I'm not seeing the benefit over exporting A, B, and C as functions, and then putting them together in another spot (like a composite root for pure DI, or an IoC container, etc).

Is the argument for top-level await that you don't need the other spot? Because I feel like you still do - except now it's implicitly inside not only A, but likely B and C as well to some extent. And in a very inflexible way.