I guess it would depend on how the story develops whether I would be amused or disappointed by an ending like that. If there were comedic elements throughout, and we got the sense that the protagonist was not really a good detective (and/or an unreliable narrator, if from a 1st person POV). I kind of like the idea of taking the trope of a brilliant amateur detective who is much more competent than the police, and turning it on its head. As I said, though, it depends on the execution.