It's probably relevant to point out that my view of authorship is based on my own experience as a professional writer.
I have extensive experience ghostwriting for other people, both in technical documents and for publication to the general reader. In the case of technical documents, the engineer, architect or planner provides technical expertise, while I organize the materials and write the information in a way that is more compelling and interesting than it might have been if it was written directly by the technical expert with little writing experience. In terms of ghostwriting for the general reader, an author will often tell me the kind of story they want to write with one or two of the elements they want to include, and then I will create a story under those guidelines, with the author reviewing drafts and working closely with me on revisions. At other times, I have been part of book projects where the "author" of the book simply gave me a genre and didn't want to read it until we were in the final stages of revisions.
In other cases, I have worked with teams of other writers and content experts, creating a larger work with so much back and forth and editing/refining of each other's materials, that is was difficult to figure out who wrote what, but everyone had a hand in the creative effort and the final product.
When I was in the magazine world, we would often use a number of freelance writers with variable levels of skill and expertise. On occasion, I would recruit a first-time writer to help with an issue because they had the connections and ability to get the story we needed. But when I would get their story, it would be a mess. I would often have to call the writer and interview them about their story and fill in some gaps, then completely rewrite the story with a new approach. In those cases, the person who brought me the story was still credited as being the author, but often very little of their original written work remained.
Therefore, I come to the question of authorship with a more nuanced view. For me, Moses did not have to write or supervise every aspect of the writing of the Pentateuch for me to consider him the author. Even if Moses did not write a single word, but the foundational materials were produced under his authority and supervision, I would still consider him the author. I would also still consider him the author if those materials were heavily edited and combined with other sources well after his death.