As @pseudobry mentions: 'the book uses GDP as a "human welfare" metric'. I don't think anybody here (even the author of the book presumably) is suggesting that

As @pseudobry mentions: 'the book uses GDP as a "human welfare" metric'. I don't think anybody here (even the author of the book presumably) is suggesting that they are cause and effect, but they do appear to be correlated. Also just because 50% have 1% of the wealth, doesn't mean they don't contribute towards the wealth of the other 50% of people holding 99% of the wealth. For example, your boss gets the majority of the profit, but they couldn't run the company by themselves.