If I'm interested in building low latency and highly available web services it seems to me that both Go and Elixir are reasonable choices. How are they not the same primary domain?

But in any case, Elixir allows a lot more clever code. In my experience working on legacy software, clever code in a dynamic language is error prone and hard to refactor and maintain. Static typing can help, though, I've found this especially true in functional languages where you have a super smart developer do something clever that's hard to understand 5 years later.