They're incredibly different skill sets. One is all about argumentation, convincing, facts, and citations. The other is all about imagination, beauty, evocation, flavor.
Obviously they both require assembling nouns and verbs and other parts of speech in sentences, but they seem to be virtually entirely different capabilities at the end of the day.
Writing excellent short stories doesn't really help with crafting effective business communications, design documents, etc. And vice-versa. In fact, I think they can sometimes even be harmful -- the kind of clarity required for non-fiction can constrain imagination in fiction, while the creativity celebrated in fiction can be quite counterproductive when it comes to functional communication -- what is intended to be clever or unique often gets misunderstood.
This is a cliche.
You can’t write precisely without an understanding of how language becomes imprecise, of its fundamental instability. Precision and delicate use is an accident when it does happen, and its happening can never be proven. We must have faith in the accident.
You can be taught to and be proficient in "writing with your pencil" by learning the rules [1]. Efficient, practical, immediately useful and applicable. No subtlety required nor desired. It's the same as all practical skills or trades.
Holding yourself to a standard doesn’t mean it’s a meaningful one.
Either way, it's an avenue of learning to write that ignores, I would say, all the artistic aspects of writing. Inasmuch as you can say anything "isn't an art."
So yeah, I recommend the book to people interested in writing.
Rhetoric is valuable in any writing endeavor; clarity is only valuable sometimes.
Though a few years ago when I searched for a book on rhetoric and making convincing arguments Office Of Assertion by Scott Crider also popped up, but it's aimed more at written rhetoric instead of what most people have in mind.
But it's much broader than that. You can make true arguments. You can make confusing arguments. And you can use tools that have nothing to do with logic at all. Rhetoric has a lot to say about rhythm, alliteration, and linguistic structure. And a lot more to say about your personal bearing and your tone of voice.