Flashy website, but a quick background check of the contributors reveals that they've barely been working at their respective positions for over a year.
In any event, kudos on providing an interesting narrative.
That's probably why they put together the content in the form of a collection of interviews. They don't establish authority of knowledge. They establish authority of intelligent curiosity.
I don't understand how a lack of documented experience correlates with the quality of this handbook. In fact, you might as well assume that W person needs X degree over Y years to become an expert in the field of Z...
Not everyone documents how long they have been in the field publicly, and for all you know (or don't know...), some of the contributors (that I personally know myself), have been immersed in the field for years.
Also, from a more credible standpoint, majority of the book has direct Q&A + perspectives of some of the best data scientists...