The books were written with a general audience in mind. So the methods that are described are ones that will work for most people most of the time. Of course, nothing in training is either/or; it’s just a question of how much when.
Our coaches are very familiar with block training methods, and we often use that approach with athletes that have multiple, and sometimes conflicting, areas of fitness that they need to build or maintain.
Here’s a list of forum posts on the subject: https://uphillathlete.com/forums/search/block+periodization/