I haven’t used Ruby much, but anecdotally I once rewrote a Ruby service in Java and was able to reduce the number of servers needed from ~100 to 10. That was a case where it was “frustratingly slow” in practice.
Anyway, obviously Ruby (or any other dynamic language for that matter) isn't the solution to every problem. I was once tasked to refurbish an old Delphi desktop application that did some thermal simulations; I wrote the interface as a Rails webapp and the simulation itself as a compiled C routine, which I called from Rails via FFI.
Anyway, obviously Ruby (or any other dynamic language for that matter) isn't the solution to every problem. I was once tasked to refurbish an old Delphi desktop application that did some thermal simulations; I wrote the interface as a Rails webapp and the simulation itself as a compiled C routine, which I called from Rails via FFI.