Isn't it possible for a dev to fulfill requirements but still deliver a bad result as measured by subjective (but important) things such as code smells, bloat, crappy algorithmic logic, and so on? Or do you think managers need to spec things out in such strenuous detail that surprises (but also, to an extent, autonomy and ad hoc decision making) aren't possible?

There's also the case of R&D roles where it's hard to spec things out exactly in advance, and you're partly relying on the employee's ingenuity.