@Mel Hopkins, I watched the video and read the article -- an interesting story. So much talent went into the GPS project over a period of decades. Today our best and brightest go to Facebook and Goldman Sachs; what a waste of talent, but I digress...
I like your advise because, you wrote, "Marketing doesn't dictate WHAT an author should write. It's just that the author should have a group in mind when they do."
An author has to, otherwise they won't sell many books because they won't know who the audience is or how to reach them. Don't believe your family will buy your book in droves -- many will want the "hook up" 😉
Of course many writers only write books demanded by the market, and that is perfectly fine.
Publishers often want to publish specific types of books because they have a particular aesthetic, sensiblity, mission, or are simply chasing percieved consumer demand. They then look for wrters to fit the bill.
Strife between writers and publishers arise when there is disagreement between what an author writes and perceived consumer demand. The impacts everthing from cover design, the book's title, and the editing process. Somtimes the publisher is right, but they often get it wrong -- especially when it comes to Black books. Which is why we need more culturally Black publishers, editors, and booksellers.