Those companies are Boeing Aircraft (153k employees, $244B market value), United Technologies (202k employees, $148B market value), and United Airlines (88k employees, $33B market value).[0]
What most people perceive as a threat to the market is when one company takes over an entire single market. And that is a problem, no doubt. But in the case of Boeing, the problem was that one company had such an advantage vertically- lose money on planes in order to make money on shipping, or vice versa, as needed. It meant it could win in whichever market it wanted to and slowly come to dominate all of those markets. The synergies of doing it all internally meant it could win at everything.
If one uses that situation as a precedent, one can start to see the parallels in many of the FAANG companies today.
[0] "The Air Mail Act of 1934 prohibited airlines and manufacturers from being under the same corporate umbrella, so the company split into three smaller companies – Boeing Airplane Company, United Airlines, and United Aircraft Corporation, the precursor to United Technologies." https://en.wikipedia.org/wiki/Boeing