One thing to keep in mind is that when producing material, a good amount of effort has to go into making the presentation coherent. I dont have the stomach to write a book, I'll tell you that much! So referring to other work, if done right, is a useful tool the author can use to keep the subject matter streamlined, touch on some deeper aspects and provide further reference for the reader, but, moving along with the book content...
Good to consider what the scope of the material is when making those critiques, but one other thing, there is a lot to be said for the basic fundamentals, which is one thing I like about how the ymaa stuff is presented. Most people dont practice them to their full extent and dont realize the full benefit of the basic things, that provide stronger foundation for the additional things to practice. (Which get practiced in between fundamentals, just about.)
Its all in the strength of your will and intent, the diligence of application, the sharpness and longevity of focus - apply those concepts to fundamental processes and make those fundamentals an integral part of your life, and then one begins to see fruit from the effort. The hard part is the diligence and time on the fundamentals, but once you see results manifest, its somethin'. Those results, like any other dynamic, can be lost, so part of training is learning how to keep that all going.
Dr Yang's approach is less directed than BK's, he lays out the fundamental concepts and its up to you to grasp them and put them to practice. Not that there isnt merit to bk's approach, it does wind up being a matter of personal preference and the ability/application of the individual, as to 'how far' either will get you
Even in mildly complex systems, any outcome is the wrong thing to target, with the process being where the focus should be.