static typing is somewhat of a programming religious wars. I mean sure, extremely weak typing is IMO horrible (python, ruby, js, I'm looking at you) but being dynamic does mean that quickly testing out an alternative code path. Just today I realized I needed to forward some information to a somewhat polymorphic data structure, a process which I hadn't planned for, I found a map structure that is encapsulated state in a gen_server in exactly the right place, so I just shoved it into the map under a new key. That is effectively breaking what could have been a static type system. And it was two lines of elegant code, no refactoring necessary, and probably a line of documentation saying that in this corner case the structure will contain this extra info.

IMO the right approach is compromise. You could do this in a statically typed system by just making everything a map... which is effectively what the BEAM languages do, but at least there's a type analysis tool that can introspect deep into the built in "flexible" types.