I've thought along those lines as well. I don't know if this helps clarify, but I did learn, for example, FedEx is actually quite strong without Amazon: "Last year [2018], Amazon accounted for 1.3 percent of FedEx’s total revenue." https://www.nytimes.com/2019/08/07/business/fedex-amazon-shi...
Amazon always shunned FedEx (used them as an option of last resort) because, unlike UPS, they refused to make changes that would be short-term beneficial but make their future outlook dependent on the whims of their biggest client.
