There is essentially no change in concentration by the top firms in the economy as a whole

See Very real progress on the market concentration debate by Tyler Cowen. 

"As you might expect, it is coming from Chang Tsai-Hsieh and Esteban Rossi-Hansberg, here is their abstract:

The rise in national industry concentration in the US between 1977 and 2013 is driven by a new industrial revolution in three broad non-traded sectors: services, retail, and wholesale. Sectors where national concentration is rising have increased their share of employment, and the expansion is entirely driven by the number of local markets served by firms. Firm employment per market has either increased slightly at the MSA level, or decreased substantially at the county or establishment levels. In industries with increasing concentration, the expansion into more markets is more pronounced for the top 10% firms, but is present for the bottom 90% as well. These trends have not been accompanied by economy-wide concentration. Top U.S. firms are increasingly specialized in sectors with rising industry concentration, but their aggregate employment share has remained roughly stable. We argue that these facts are consistent with the availability of a new set of fixed-cost technologies that enable adopters to produce at lower marginal costs in all markets. We present a simple model of firm size and market entry to describe the menu of new technologies and trace its implications.

This is likely to prove one of the most important papers of the year, here is the pdf link.  The authors open with the example of The Cheesecake Factory, and also health care:

The standardization of production over a large number of establishments that has taken place in sit-down restaurant meals due to companies such as the Cheesecake Factory has taken place in many non-traded sectors. Take hospitals as another example. Four decades ago, about 85% of hospitals were single establishment non-profits. Today, more than 60% of hospitals are owned by forprofit chains or are part of a large network of hospitals owned by an academic institution (such as the University of Chicago Hospitals).

And:

…rising concentration in these sectors is entirely driven by an increase the number of local markets served by the top firms.

Here is a key point:

…we find that total employment rises substantially in industries with rising concentration. This is true even when we look at total employment of the smaller firms in these industries. This evidence is consistent with our view that increasing concentration is driven by new ICT-enabled technologies that ultimately raise aggregate industry TFP. It is not consistent with the view that concentration is due to declining competition or entry barriers, as suggested by Gutierrez and Philippon (2017) and Furman and Orszag (2018), as these forces will result in a decline in industry employment.

This is interesting too, and it departs from say what Amazon is doing:

…we show that the top firms in the economy as a whole have become increasingly specialized in narrow set of sectors, and these are precisely the non-traded sectors that have undergone an industrial revolution. At the same time, top firms have exited many sectors. The net effect is that there is essentially no change in concentration by the top firms in the economy as a whole. The “super-star” firms of today’s economy are larger in their chosen sectors and have unleashed productivity growth in these sectors, but they are not any larger as a share of the aggregate economy.

The paper is titled “The Industrial Revolution in Services.“"