> I usually assume that […] the tool doesn't suit every problem

My expectation: inexperienced FP is trying to shoehorn a mutation-based approach into a framework that performs best with immutable data, or is manually recreating familiar structure (for loop) instead of using the idiomatic way.

But what do you tell someone in this case? They really need to learn more about the basics. Which is how I am interpreting the GGP’s dismissive-sounding comment.