To summarize, the authors use a terrible design hypothesis, and make ever-escalating claims of certainty from two weak observations.
Consider a box with an internal divider such that the box is divided into two separate compartments, A and B.
As Darwin argued, “we can hardly believe that the webbed feet of the upland goose or of the frigate-bird are of special use to these birds.”
Examples of so-called “convergent” evolution are ubiquitous, including the camera eye design shared by the squid and human.
Today our knowledge of the eye’s design is far more detailed. Particularly striking are the incredible mechanisms at the molecular level.