I have a hard time understanding the author's point of not using UML but somehow boasting that they used "plain old boxes and arrows" to create "plenty of diagrams". UML is nothing more than a bunch of "plain old boxes and diagrams", but which have concrete, objective meaning that has been specified and thus help share ideas as objectively as possible. UML is a language, and languages are tools to communicate and sha…
Normally, at a high level, where people are architecting, what is more important is flow of information and containment of responsibilities. UML is not really designed for describing these situations, and trying to wedge this type of information into a UML diagram can get confusing and can encourage architects to focus on the wrong things.
When people say "box and arrow diagrams", I think that to mean boxes=infomation+responsibilities arrows=information flow.