From a point of view between Wittgenstein and Feyerabend, one can propose this criterion: competence is competence to the degree that it is effective, there is no shared notion of what 'effective' means, but in the end it is obvious.
From Wittgenstein -- human experience is not part of a consistent whole, but is instead organized into sets of overlapping 'games' where we get continuous feedback about whether what we are doing, thinking, or being is 'right'. So there are not really enlightened or ignorant individuals (of equal intelligence) there are only those more or less attuned to the games they are expected to play.
From Feyerabend -- Since games evolve over time, no game ever really completely captures the proper perspective on any issue. If it did, it would cease to be interesting to play, and would no longer be attractive to humans. It would simply end. Therefore we are always somewhat wrong, except about things in which we are wholly uninterested. As animals, driven to some degree by a will to control things, we will always be interested in what is effective. So this is a game that we cannot allow to converge, and it won't.
From basic biology -- At the same time, we are strongly evolved toward knowing what is and is not effective. It is obvious, even if we cannot express it or agree upon it, because insensitivity to it would be quite devastating to our chances of surviving.