Actually you'd be surprised at just how fast the BEAM passes messages, especially as it also includes linking, monitoring, cross-process, cross-system, among other features. When creating a multi-thread atomic messaging system in C++ long ago I was able to out-perform the BEAM (though I'd not rank it as significantly out-perform), but once I added failure handling features among others then it never got close to BEAM's speed again in raw message passing.

However, the BEAM is not very fast on executing actual code, it is like Python in that way where it is good to slave out CPU-heavy work; the BEAM is built for async IO, and yes, running a JVM (or C++) system as a node on a BEAM mesh is fantastic for that (or a port, or NIF for small work).