One reason not to use Elixir is the absence of vectors/arrays. Yes, you can import them from Erlang but they ain't pretty. Elixirists try to pretend that lists and tuples are all you need but Elixir's lists are Lispy lists, not the Python variety. It's one of these small print things you only discover after spending time with Elixir but it can be a deal-breaker. Ask on the Elixir lists and you'll get some very defensive responses which basically add-up to vectors/arrays being difficult to optimise in a dynamic functional language. String processing is also not quite as straightforward as in Ruby and Python due to how Erlang/Elixir uses binary representation.