It is difficult to update your priors with this book: countries are left out of analysis for no clear reason (Poland, Korea?), graph axes are missing units, and the mechanisms proposed by which inequality does harm such as stress are unconvincing at the scale proposed.
This is of course an ideological battlefield and Wilkinson and Pickett’s work has received no less than three books rebutting it in turn. They would have done well to argue a more nuanced point than forming a theory of everything.