In addition to what Jim and Ariel said, I too disagree with the idea of comparing different authors, especially well-known and respected ones, and separating them into researcher/dealer category. The same goes for generalizing curator vs dealer level of knowledge. There's no point in it.
Not many people realize the extent of Oliver's knowledge. I wish I'd have a fraction of it. As for his last book, it is a coverage of collection by design, and Oliver did a great job, much better than most of us would be able to
