That's because you've learned imperative coding first. If you learned functional coding first you'd probably find imperative coding complex. I'd certainly rather code in OCaml than C.

A growing number of super-performant API servers and websites written in Elixir / Phoenix say hello.

Your first statement is unequivocally false, as evidenced by the myriad of people and projects using purely functional languages, let alone non-pure functional ones.