Internationally, a lot of places don’t accept Amex because of higher fees.

Every Amex cardholder knows to carry a non Amex card. You wouldn’t lose business by not accepting them and some vendors don’t even domestically.

I can’t find stats for other cards. But here is the average wealth and income of Plat holders

https://monkeymiles.boardingarea.com/whats-average-household...

Amex cardholders are the highest earners in the industry.