Earlier quoted context omitted.
I don't understand these reward schemes. Surely they are being funded by higher merchant fees, which means merchants charge more, which just means that the rewards are a transfer scheme between people who pay by cash/unrewarded cards and those with rewards cards.
There's a lot of truth to that (cash paying customers pay the same, even though the cost to serve them is less). But unrewarded cards aren't really any different. Most merchants still have to pay the same high fee for them. Since the bank/processor is going to take the maximum amount of money they can regardless, and most merchants will have to pay that full fee regardless, you might as well use a rewards card over a…
American Express cards offer the best rewards, but the cost to the merchant is much greater. Many shops or restaurants don't accept AmEx, and sometimes those that do will say they prefer you to use an alternative card.
But within one network, I think it's correct that the cost is the same regardless of the card's promotion.