I think it can be done, but as you say one does have to question why it is being done. I suspect actually that sometimes it is done entirely by accident - the writer honestly never realised they hadn't named their protagonist clearly. This can be an especial risk if writing in first person. It is the sort of thing that a professional editor would pick up on and correct. A beta who received the email saying 'here is my latest Willow fic!' might never notice themselves.

The only book rec I sort of have is John Gardner: The Art of Fiction although he can be unbearably pompous, and I wanted to throw him through the window at times for his attitude to professionalism (amateur writers aren't allowed in his world view). But he does have some useful stuff. I can definitely warn you off Stephen King On Writing which is a complete waste of time and money. Since they are more or less the only books I've read on the subject I can't help any further.