On a related note, there are a _lot_ of indices. FT reports that there are over 3 million stock indices, for ~50k public stocks [0]. You can make an index with basically anything in it. There are indices for emerging markets, for the Gulf region, for companies in Mexico, for companies which qualify as ESG (environmental, social, and governance) criteria. There are indices of stocks that historically perform well in periods of rising interest rates, and there are indices for the Eurozone.

The ETFs just build on top of the index. In almost every prospectus, there is some kind of note about which index it is. You can go look at how the index is arranged, and there are sometimes multiple funds that track indices in the same sectors, with different weights. If you're not happy with the amount of Berkshire in your financials ETF, you can go find a fund which uses a different index and buy that instead.

If anything, a stock market index is _more_ valuable in a digital world, because it effectively adds a layer of abstraction to the typical notion of investing.

[0] https://www.ft.com/content/9ad80998-fed5-11e7-9650-9c0ad2d7c...