> the author completely avoids the thing that is the most brain expanding and thrilling part of drawing which is learning to draw from imagination rather than copying or tracing photos

All the drawing tutorials for beginners I have seen putted a lot of emphasis on drawing from refences first, before you draw from imagination. The reason stated again and again was that you need to learn how the object looks like before you can draw it from imagination - that people do not know how objects really looks like unless they trained it first.