Not all Amex cards have fees.
Also it would have been nice if the author went a little into the history like how Discover was once part of Sears. Not sure if this is still the case or not, but the classic Green, Gold, and Platinum cards are charge cards and have to be paid in full each month. Some of these things may explain why Amex is more affluent.
Airport lounges, concierge, exclusive books on Michelin star restaurants (also via Tock acquisition), etc.
Repeat every quarter.
There are at least two cards with useful quarterly bonus categories.
The overhead is no more than swapping out the cards in the wallet every 3 months and try to remember what the categories are. That's not even necessarily if you regularly use digital payments (and of course if the merchants support that).
(And I believe most people never hit that $1500 cap in specific category. If you do, like, spending $500 on restaurant/Amazon/Costco a month is like nothing to you, ignore everything I say)
I'd say the overhead is much much lower than things like "digital coupons" offered by grocery stores -- those are truly aimed at low income shoppers who are willing to spend time doing that.
I don’t know that I am a stereotypical Amex cardholder (member since 2012) but I certainly love perks like that and will always check for FHR listed hotels when booking travel.
Reality is that you want a couple of benefits, maybe airport lounge or late checkouts. That's not worth the Platinum card fee -- but if you are saving $25/month with Uber, getting your free Four Seasons breakfast, Hilton Diamond, Marriott Platinum, etc, suddenly you're making money by paying $1000 for a charge card. For me, I pay for a Hilton and Delta card. I basically end up with a completely $0 3-5 day getaway annually, with a value that is well above the baseline 2% cash back.
Other brands charge lower fees, but make you use captive portals for travel. Sometimes that hurts your earnings with the hotel and airline programs, which is meaningful to some folks. Personally, I find value in having airline and hotel "status" for preferred boarding and little perks.
My salary is decent enough compared to the general population (>$200k yr), so does my SO. But when we travel it never occur to us to check FHR -- those places are too expensive, and we didn't see value in those "perks".
Chances are that your income is much higher than mine, or at least you are much more willing to spend even at the same income level.
They changed this a few years ago with the "pay over time" feature on those cards.