Here are the author's examples:
>McDonalds and Burger King
McDonald's is far larger than BK. Also Wendy's is larger than BK according to this source: https://www.qsrmagazine.com/content/qsr50-2017-top-50-chart
>GM and Ford
Another non-example. We just gonna pretend toyota doesn't exist?
>Nike and Reebok
Again, wtf? Even when reebok stood alone, there was still Adidas in the picture. Not a duality
These examples were picked in the early 1990s, and are specific to the US market. Things change.
For example the US car market has long been largely dominated by GM and Ford with Toyota only recently breaking that (and VW is non-existent). GM and Ford are still the two largest manufacturers: https://knoema.com/infographics/floslle/top-vehicle-manufact...
The point is that there is usually very few dominating brands in a market, with the top 2 (approximately) yielding the power and the others following and filling the gaps.
...like whether that claim is well founded or not.
The worst mistake we engineers tend to make is to dismiss the 'wisdom' of professional marketers and branding experts...
Sure there should be charity in reading but the default assumption is not that your examples are 26 years old. Many people here were either children or not even born yet.