The Writing Problem of Omniscient Detectives

Too many writers of detective fiction want their detectives to be super super smart, which they translate as omniscient.

That is, they misunderstand Sherlock Holmes. Sure, Holmes is nearly always right--but it's a right that has been tested. Like Monk and Sherlock from Elementary maintain, guesswork is just guesswork. Without proof, the guess remains a guess.

The brilliant mindset is a separate phenomenon and kind of irritating. It also creates a writing problem.

In Marsh's Singing in the Shrouds, the insightful, intuitive, etc. etc. Alleyn suspects the bad guy. How could he not? He's so smart! 

And yet for the sake of a dramatic climax, he leaves the suspect unwatched. The result is a death. In the text, Alleyn admits that he blundered. But this isn't a blunder. His actions are gross incompetence IF Alleyn had the claimed suspicions in the first place.

The problem of wanting perfectly wise characters who nevertheless mess up leads to annoying plots where characters who should be fired are treated as victims of an unkind system. But the "solution" to the mess-up happens because the writers want them to know more than a reasonable person would know--to be all that.

There is a variation on this archetype: the detective who knows but doesn't act because to act without proof is morally wrong or a waste of time (Columbo, Poirot, Sherlock, Gibbs). Unfortunately, too many of the omniscient detectives, like Alleyn, are praised for their intuition--that is, they are expected to trust to their brilliance and yet...

Dead bodies.