This time the short answer is, it doesn’t matter.
The cover does not illustrate my book, it advertises my book. A good cover sells the book to people who will like the book. A bad cover either doesn’t sell the book to the right people or (worse) does sell it to the wrong people.
The worst sin an art director can commit is to forget that the purpose of a cover is to sell the book. There are books which would be better served with a garishly colored pulp cover–for example, a blonde in a torn dress being threatened by an Oriental with a dagger–than they would by a brown-and-gray wash of sad people in a grimy alley. Nonetheless there are art directors who would be embarrassed to put the right cover on that book, because their artistic friends would laugh at them.
In this case as with the writer/artist relationship above, the book loses because of personal benefits to one of the parties involved. That’s the way life is.
I generally have opinions about art and covers, but I almost invariably keep them to myself because I know that I’m ignorant. The flip side of my attitude is that I have a broad vocabulary and know quite a lot about prose. Editors (and more often copyeditors) who meddle there are likely to find that they have a problem.