It cannot possibly be BS in absolute, because people teach other people how to use these skills better, and books can genuinely be used to guide people on how to do the task better. That's essential to the idea that this is a skill and a body of technique, not an ineffable revelation that can never be discussed or shared.
This isn't Buddhist nirvana, where the end state is literally beyond description (incapable of being understood within the five aggregates) and only transcendental enlightenment can give you any answers. It's a skill, it involves a body of technique that can be expanded or improved, and collection of knowledge that can be communicated in better or worse ways. We can identify important elements of that skill. We can create, modify, and eschew various techniques for practicing that skill. And we can improve how we communicate about that skill, how we collect, condense, preserve, and transmit the knowledge of previous generations of practitioners to future generations, so they can harvest the fruits of their forebears' labor in days, weeks, or months as opposed to lifetimes.
Running a tabletop roleplaying game should not be relegated to an ineffable burst of insight with no ability to speak it to others. It should not be reduced to mere intuition without concept or structure. It should not be confined to the auteur avant-garde GM plastering the world with nigh-incomprehensible modern art.
It should be recognized for what it is: a skill. Skills admit training, practice, evaluation, and improvement.