I think it's nice that you can run everything in the same server. If you're scaling, and want to split everything up, that's a "nice problem to have", but it's convenient if you can just run everything in the same application/codebase when you're getting started.

I do agree with you that's not a huge win compared with Rails, but it is nice to have. I think you'd have to look more at something like "lots of concurrent, long-lived connections" for the real wins over Rails for the BEAM ecosystem. I mean, you can do that in Ruby if you want to, but it's going to be cleaner and simpler with Elixir/Erlang.