I agree, but sorta in both directions—which paints a great contrast between product (design or management) and UI design.
I really enjoyed the book and think it's great entry to a design mindset. This is a mindset for how to make products that work well and people like or would actually use. Is that what we expect of a designer or a product manager? Important, but just a bit downstream of that is how it works and where the buttons/interactions are and whether people think its attractive. Most designers (we can confine this to tech [1]) consider themselves product designers rather than UI (or even UX) and often have that title and the bullet points in the job description to reflect it. That is, they want and are hired to understand users and design _products_. And then later, design _interfaces_—but only later because ofc the interfaces should derive from those things.
You can argue, for various reasons [2], a majority of today's tech designers would not be good at making product decisions (which includes the processes of understanding users or designing products); to which I would mildly agree, but find more pertinent to then immediately question why recruit and hire someone with that offer. You could hire directly a UI or visual designer.
In practice, because of power dynamics, most designers design UIs and some UX. There is indeed time spent on the product work that the designers feel they should be doing as part of a "real" process, but doesn't ever land in the product. That work is done genuinely, but frequently amounts to design theater—both internally to their own teams/companies (which "storytells" the work) and externally when they present their portfolio to others [3]. Most product (design) decisions are not made by designers because they're either not present for or can't win any of the upstream arguments. So even at the UI level, where there is more control, the design is based on "received" constraints.
Anyways, I think your comment is a real good provocation for what do we mean by designer or what should a designer be.
[1] I think this applies to plenty of folks called a designer pre-tech, say, industrial designers or architects.
[2] There are many, but one is simply that designers who are capable at this, find that design is not the place to impact them. They should perhaps become a PM (which is full of its own pitfalls) or found their own company. Or more commonly become a disinterested designer. I'm not sure either role, PM or design, is able to really do this well in the way most tech companies are organized, but the PM is in many cases the designer's real informal manager. And the informality is the problem. They have more power, but not any hard responsibility for/to the designer. And so you get a junior and/or apathetic pool of designers.
[3] Most portfolios, if you're not familiar, present designs as designed (what was made in the design tool) not as implemented (screenshots or the actual live app) for a reason. And further, most