The book's shortcoming is that even though the married author advocates not marrying, it lacks persuasiveness.
Literal
This-book [possessive-の] shortcoming [topic-は], married-person is author [subject-が] non-marriage [object-を] even-if-recommends, persuasive-power [object-を] lacks thing is.
A carefully constructed critical sentence. である appears twice: first identifying the author as 既婚者 (married person) in an appositive clause, then closing the topic-comment structure. ~ても concedes the point ('even though the author recommends Y'), while 説得力を欠く delivers the criticism. 本書 uses the formal prefix 本~ meaning 'this book.'