What are you talking about, its like an order of magnitude faster than ruby? It might not be as fast as Go or Java or whatever, but its not even a comparison to ruby, and particularly rails.
In that case, the multithreaded nature of Elixir and the VM there's no comparison.
I tried searching for raw ruby+erlang benchmarks but couldnt find much in the short time I looked.
If we're talking about pure ruby and elixir, things become complicated, you can do some stuff a bit faster in ruby sometimes (where ruby is using native optimized C code)