The first, and most obvious question regarding that statement is by what criteria is that judgement made? Obviously, it depends upon what is one's purpose in reading a book on the subject of Taijiquan.
One possible purpose to read such a book is to acquire academic knowledge regarding the art. That knowledge can include its history, its origins, its goals, who were the notable figures in its history, influences that might have shaped its development, its general strategy as a martial art, its philosophical underpinnings, and so on. Those are academic aspects of the art. Many books have been written on those subjects, many quite successfully: they impart academic information regarding the topic.
Another possible purpose to read such a book is to develop actual skills in the art - in contrast to knowledge about the art. Many "how-to" books have been written. In my opinion and experience, it isn't possible to effectively learn the practical skills of the art by reading about them. As I've previously stated elsewhere, this is due to the art being experiential and the failing of words to adequately and unambiguously capture or describe that experience. There is far too much room for incorrect interpretation for most readers to obtain a "correct" physical interpretation and implementation of what is described in words. For THAT purpose, in my opinion, books have very little effectiveness and are largely a waste of time, effort and money.
In my opinion and experience, those who don't already have a good grasp of what they are reading regarding the physical interpretation and implementation have their heads filled with buzzwords the meanings of which they do not understand, but can then repeat them as if "in the know". Some teachers are very secretive about what they teach in order to prevent non-students from "stealing" their buzzwords, the result of which is "everyone" now talks about said buzzword, but few know what it means or how to physically manifest it.
In short, it depends upon where one is in one's progression what books might be of value. Even then, their primary value is to remind one of points that one learned during hands-on teaching with a skilled teacher, or, perhaps, to phrase the same thing one learned during that hands-on teaching in a different, possibly, more accessible way. What one reads is, in my experience, familiar guideposts along the way. If one hasn't already encountered those guideposts in hands-on teaching, the guideposts are either unrecognizable or unintelligible.
In earlier days of my practice, I did a fair bit of how-to style writing about Taijiquan. I realized that is was largely a wast of both my time and those who read it. While it helped me organize my thoughts, it did very little to help those who didn't already know learn to do what I wrote about: it was largely a fool's errand for both author and reader.
Largely unimpeachable sources of written information are the "classics" of Taijiquan. Unfortunately, again, until you already know and can do what they describe, they are largely unintelligible and open to many, many interpretations, most of which lead students in the wrong direction. For example, an often stated admonition in the classics is to "sink qi". As you are aware, what "qi" is, and how to "sink" it, have many interpretations and physical implementations. There are no shortages of more modern written descriptions on what qi is and how to sink it. There are, however, relative shortages of skilled practitioners.
One of the books that is important to me is the English translation of Hong Junsheng's book. However, it, too, would be scrap paper without hands-on training to understand what he was attempting to describe.
Another book, one that I read a long time ago, but I recall finding useful in a guidepost-sort-of-way, is Taijiquan Through the Western Gate, by Rick Barrett. In his book, he writes the following:
An old Chinese story goes something like this: A fish was hanging out by a pier when he heard some men talking about water. This intrigued the fish. He had never heard of this remarkable substance. He returned to his kin and announced he was off on a quest to find this mysterious "water". He was gone a long time and hand many adventures. When he returned to his family, they asked if he had found this mysterious thing. He said, "Yes. But you're not going to believe this..."
Another book, on the basic standing of Yi Quan, is The Way of Energy by Lam Kai Chuen. It provides guidance on the physical standing postures and attempts to provide some description of the sensations one encounters during the practice.
I have no doubt that others have found books that they have found "worthwhile" and encourage them to post those and why they though they were worthwhile. (It would be a much longer list of not-worthwhile books, but that would not be a particularly productive list, other than what one might want to avoid.)