I know Matt pretty well and it's important to understand that he's a writer first...then a runner/triathlete. He makes his living selling articles and books. His talent lies in writing; if he were to have earned his income through running, he have had a hard time. Like so many others, without this pressure to perform, he's altered his "training beliefs" with each passing year (and each subsequent book). "Studies show" is a primary line of his, and those who have known him for years poke fun about his ever-changing stance on how to train. But we understand implicitly that he's out to sell books and respect that immensely; he does this successfully.
Years ago he had a hard time understanding why it took so much running (or, in the case of triathlon: running, swimming and cycling) to achieve desired results. I think he felt that most of what these athletes were doing wasn't "training" so much as appeasing their compulsions and addictions. It was not easy to get Matt to listen, so we didn't try. It seems ultimately best that athletes learn the hard way, but in his case, as it is with so many others, the years caught up to him and his best races are now well behind him. All because he didn't believe in greater training volumes.
Americans in particular like to search for easy solutions and magic bullets. But in endurance sport, there is no easy way. Lydiard said this very thing back in the '50s for crying out loud! Still, we search for the shortest of shortcuts leading us to the top, a notion that already goes to undermine our toughness (which, along with motivation, is the key ingredient for success in sport).
The 80/20 rule isn't exact, nor is it true science, but if you delve into it, you'll see how accurate the premise is at the top tier. But it all comes down to embracing a substantial amount of chronic training volume, or it makes no sense whatsoever. Those expecting to reach their best by doing the least amount of work (or the wrong work, ala the cross-fit nonsense) will, hopefully, see their flaws one day, before age has caught up to them and its too late.