Elmore Leonard is definitely a literary writer. Oddly, that’s only even a question in the USA. But as to which format the backlist should be in, I’m not so sure. A lot of people - me, for example - first discovered Elmore Leonard in mass market paperbacks. But then, there are a lot of “literary” readers who would really appreciate the books if they read them. Maybe trade paperbacks are the way for them.
Actually, I’d like it if some of those older books would be reissued in hardcover. I’ve seen hardcover copies of Unknown Man #89 and Swag selling for over five hundred bucks each. I realize the collector’s market only wants first editions, but there might be enough people interested now who never had a chance to buy the hardcovers when they first came out.