His book is basically taking Duckworth and Dweck to the masses. It is a good primer for those too lazy to read and research themselves or to new coaches who are still think they're all that because they understand basic physiology.
Magness gained a lot by adding Stulworth. He is more of a writer and it helped with the flow of the book.
Magness does know a lot about physiology and has an inquisitive mind. He is obviously intelligent.
That being said, he knows he is intelligent yet doesn't understand that he isn't in a stratosphere where common coaches don't get him. He can come across as condescending on twitter.
He also is a bit hypocritical doing the l carnitine test and then trying to become the face of integrity. I am 100% certain he is intelligent enough to have known that was wrong and questionable beforehand.
Finally, he badmouths certain coaches - particularly HS coaches in Texas - and it affects his ability to recruit.
I think he probably means well and desperately wants to be viewed as helpful and knowledgeable. He has some things to work on (don't we all?) - his public persona being one of them.