I think there's a "no true scotsman" fallacy lodged in there somewhere. The fact you even wrote that writing benefits from humility indicates an acknowledgment of good writing is made better by humility, and maybe then we just move the definition of "good" to be requiring of humility.

Someone may be able to write, and get a point across, but it's not just the wording and explanation, it's the capture of the context within the writing, and without humility the context is likely to be distorted, thus negatively effecting the goodness of the writing.