I wouldn't say "better". Like any other framework, many things have to be weighed. In the case of F#, it's a fantastic language with a fantastic runtime. It is still "windows only"* for the moment though. Akka (and yes, I realize that you mentioned .NET) is also very good in its varieties. Scala being one of the ones that I've actually used. I believe where the sweet-spot is for Elixir, in general is that Rubyists will feel mostly at home. The language itself is just very, very nice. Phoenix continues this by copying some of the nice ideas from Rails. But again, It's not better than the language and tech that you mentioned, but it fits a certain swath of developers. I wouldn't recommend someone who is well versed in F# with Akka.NET drop what they're doing to migrate.

*Yes, I'm aware of Mono, but I've been completely unhappy with my experience using it.