"Most (all?) large systems developed using Erlang make heavy use of C for low-level code, leaving Erlang to manage the parts which tend to be complex in other languages, like controlling systems spread across several machines and implementing complex protocol logic." (quoted from the Erlang FAQ).
https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
Saying Erlang is slow is like saying Ruby is slow. But both are built for problems other than crunching numbers. Not a knock on either language.
Crystal is built in the same vein as Nim - meant to be as quick as C++ but easier to write. Erlang was built for a different use case altogether.