> Actors can be made to do structured concurrency as long as you allow actors to wait for responses from other actors

At which point they're very much not actors any more. You've lost the deadlock avoidance, you can't do the `become`-based stuff that looks so great in small demos. At that point what are you gaining from using actors at all?

To adapt the analogy from the link in the root comment, this is akin to saying "`goto` can be made to do structured programming as long as you strictly ensure that the control flow graph is reducible". Which is to say, it is a true statement that manages to miss the point: the power of both structured programming and structured concurrency comes from defining new primitives that fundamentally do the right thing and don't even give you the option to do the wrong thing, thus producing a more reliable system. There's no "as long as you...", it just works.