Actually no. There is a lot you could do to make it easier to reason about that function. Just because you picked a poor type signature does not mean that Haskell is fundamentally limited. By making the signature a.) More generic and b.) restricting behavior through the use of better types you could achieve exactly the expressiveness you are looking for.

Also, while we may all choose to "trust" the C++ standard library, where it really comes in handy is reasoning about code written by your team on a day to day basis and being able to quickly re-factor code you did not even write.