> If languages like Haskell and Erlang gave a competitive advantage, wouldn't we see companies which used them succeeding over those that don't?

Like these?

https://www.haskell.org/haskellwiki/Haskell_in_industry

https://www.erlang-solutions.com/industries

https://ocaml.org/learn/companies.html

http://fsharp.org/testimonials/