> All that said, I see no problem with using a convenient designation to refer to a hypothetical author.

And that is -- it's not terribly convenient if it distracts the under-informed reader about the provenance of the source material.

In this specific case there's the insinuation of authority by proximity / familiarity.

While it's a convenient designation, continuing to imply the author of the primary source of the new testament was someone we can identify gives it more credibility than attributing the story to an unknown source, or an amalgam of sources.

Compare and contrast, say, Greensleeves -- a piece that everyone in the UK and AU recognises as indicating soft-serve ice cream is in the area, where the composer / author 's actual identity is at best secondary -- attributing a work of fiction to a (likely wrongly) named author grants credence that may be inappropriate.