I think you slipped in a subtle but annoying mistruth here: "in the overall universe of problems those domains are rare" is just not true. What is true is that

I think you slipped in a subtle but annoying mistruth here: "in the overall universe of problems those domains are rare" is just not true. What is true is that the kinds of programs Go programmers typically write may end up not needing this sort of polymorphism, which is very different from saying "domains where this sort of polymorphism is important are rare". I only point this out because I've seen a lot of Go programmers defend Go by saying parametric polymorphism is only really important in particular niche domains, when really they want to say that Go only focuses on a particular niche domain where it isn't important.