Derivative works aren't really the primary problem copyright law was created to address. In the early days of novel publishing, it wasn't uncommon for a popular book an author had sold to a publisher on a royalty basis to just be reprinted by other publishers who kept all the money for themselves. It wasn't unheard of for the majority of an author's books to be published by people who weren't giving any money to them until the law stepped in.

I think people have a tendency to focus on corporations and super-successful individual creators as the primary beneficiaries of copyright, and I get it, but George R.R. Martin should not be your yardstick: the long tail applies here. A lot of authors have books that might keep bringing in a thousand dollars or less a year in royalties over a couple decades; if those authors are able to put out a book a year, that "back catalogue" might end up being most of their writing income. And the rise of ebooks has probably created more authors in that boat, not less.

The original US copyright act in 1790 set the term at 14 years, with a near-automatic extension of another 14 years granted upon request. I'd be happy enough going back to that, but I don't think I'd want to see less, honestly.