I think what the author is trying to point out here is that in the world we live in today the stock market indexes are less valuable. Stocks used to be able to be bought using technicals like the P/E ratio and other financial tools. As companies like facebook and snapchat and the likes. Companies whose values cannot really be calculated by the assets they hold (land, machines and factories etc). Their value is in their Brand, their IP and other subjective articles. But they are listed in the stock market and they dominate the stock market today. It generally makes these tools weaker in calculating the value of the market using stocks which was created for an industrial age