I've never heard of this fellow, but I really like his ideas. Great website, thanks for bringing it to our attention. I've come to some of the same opinions about breathing he has, but he's put into words and action a whole breathing methodology. Pretty cool stuff. And much is old wisdom. I'll be spending some time going through the site.
As to why we don't hear more of things such as this - money. There is no way to make any significant $$ from teaching one how best to breath. There should be, but there is not. It's some priceless advice. Much about improving health and longevity is free, but mundane, including DIY life advice and many (mostly plant based) generic substances. The world only wants to market to you, not necessarily help you.
I came at breathing technique from several other vectors. 1) Hearth rate variability (HRV) score to judge adequate recovery from exercise. Paced controlled breathing is one thing that improves HRV. 2) full lung breathing is essential to cycle as fast as possible - an activity near and dear to my daily existence. 3) I take a lot of supplements. I 'feel' that to ingest various supplements into the body without using breathing to improve exercise to get excellent blood flow that forces nutrients and molecules into all body tissues, is just a waste of supplements. They could simply have no useful effect, or worse, be dangerous.