Eh, it really depends. Some people find trees easier to navigate through recursion than iteration, same for lists and graphs. Some do better using decomposition on a list to get a combined value or create permutations than doing it through iteration and indexing. FP commonly becomes problematic when things are far more trivial to do stateful than stateless, with side-effects than without, and more.

FP usually shines in small sections of easily isolated code, where it is still trivial to grasp for most and its strengths show more than its weaknesses. Given that code isn't more easily expressed using iteration, anyway. The moment things have to be woven together and not leave any side-effects is when the difficulty jumps to 11.