The book is quite good for elementary distributed systems theory. You would not want to design sophisticated systems from nothing but the principles in that book but it does a nice job of outlining the areas of theory that you need to understand in order to excel at it. Each of the chapters hints at topic areas that require a much deeper dive if you want to master distributed systems. Like Wikipedia, it is merely a starting point. For example, the discussion of greedy routing theory barely scrapes the surface of what is known about designing distributed system with approximately optimal aggregate system throughput.

You can get by in many cases without fully understanding the topics in this book. Most popular distributed systems that exist today ignore fundamental concepts in at least one of the theoretical areas discussed. But that is also why distributed systems tend to be brittle or exhibit mediocre scalability. The book doesn't fully explain why some of these areas are important but if you study each of the subject areas, it will become obvious.