Yeah, other books aren't so useful really. Dearing not only gives a very deep repetoire in the strongest lines, but against important or common lines, offers more than one alternatives, and even briefly covers lines he doesn't recommend to give you an idea of some other options. Other books on the Dragon are way too outdated to be recommended. Even the lines in Ward's book are too old and have been shown to be not so good these days. The only other book I could think of to recommend would be Steve Mayer's book on the Soltis Variation, but Dearing takes the best lines from that book, and puts it in his, so it would be redundant. Just buy Dearing's and master it, and you won't need anything else. That's game-set.