Is it? The book requires being quite familiar with programming already. Perhaps this is me projecting my own experience of when I read it, but I feel like the book is targeted at someone in the late-phase of being a Junior Dev, and/or the early-phase of being an Intermediate Dev.
I personally derived a lot of value from reading the book, and I feel like my skills noticably improved from before to after. So perhaps my own biases are showing, but I believe discounting the book's contents wholesale is a mistake. There is a lot of value to be garnered from reading it. The book doesn't have to be the infallible word of the Software Gods for it to be useful.
That disclaimer filters out anybody that isn't at least on the transition to be a senior dev (with real seniority, not just in inflated title). It takes quite a lot of experience to agree or disagree with a rule, and respect a point of view without automatically applying it.
In fact, since the rules on the book have way deeper impact than they look like, being able to read that book and not getting damaged by it is a good test for seniority.
But, funny thing, if you are mature enough to fit the disclaimer, you've necessarily already seen all that the book talks about and don't need reading it.
I personally derived a lot of value from reading the book, and I feel like my skills noticably improved from before to after. So perhaps my own biases are showing, but I believe discounting the book's contents wholesale is a mistake. There is a lot of value to be garnered from reading it. The book doesn't have to be the infallible word of the Software Gods for it to be useful.