Earlier quoted context omitted.
It's a good question. Let me meditate on actors and STM. Perhaps there's a way to get something like vectors that's composable.
The point of the actor model, at least in OTP, is not to have the actor model as a unit of computation (as was imagined by Hewitt, et, al) but as a failure domain . Erlang was not designed to be an actor system, it was designed to be a robust system and they later discovered that what they had built was more or less the actor model (if an impure version) and it was easy to communicate the architecture's computational…
Then the idea of adding a supervising and observability was a natural addition to these systems.
That said, I think OTP is a great tool for modeling failure domains and I think it does a great job.