I don’t think so this is the same league to compare this two langauges 
Elixir is dynamic, strong pure functional language vs static typed OO C# (maybe with some functional aspects). C# is more close to Java for me. C# is not even close to Scala. In Scala league is F# from Microsoft Family.
Except this Elixir runs on Erlang OTP actor model The actor model in 10 minutes. You could get the same if you run your C# code in Akka.NET
But I think I agree that you can do more in C#. Elxir/Erlang is specialized to write robust distributed/web systems. It is good to know what tool use for task
My 2 cents about OO mutable languages. It don’t like them at all. It is very hard to reason about flow when you mutate data. And is very hard to write concurrent system using for example threads when you need to secure access to common data. And even in OO they say “use composition over inheritance”
My conclusion:
You should know at least:
- one OO language
- one dynamic language
- one functional language
The best idea is to learn every year new language
Except this one cloud platform Amazon WS/Microsoft Azure/Google Cloud Platform 
About functional jobs, I think not so bad
