As a result, the American Express API is actually decent[0].
[0]: https://gateway-na.americanexpress.com/api/documentation/int...
You could write personal checks, but not every business accepted them and if you were a business there was a period of days, sometimes weeks where you didn't know if a payment was good. I did pizza delivery in the 1980s, we accepted cash or check and I would guess about 1 in 10 checks were no good. That's a huge loss to absorb. And drivers would make occasional mistakes handling cash.
I remember when Visa and Mastercard started to get popular and widely accepted. Before that you had store credit cards, gas station credit cards, you were carrying around maybe half a dozen different cards just to do your normal purchases, or you were writing checks everywhere. e-commerce didn't exist yet but it would never have been possible paying by cash or check.
Visa/MC and later Paypal, Stripe, etc. solved real problems and provided real conveniences. That's worth something.
If you think about it.
Stripe, Block, PayPal only exist because of credit card networks (Visa, Mastercard, American Express, JCB, Discover) and issuing banks (JPM, WF, BoA, foreign banks). Those last two groups of entities have such terrible integrations/interfaces and fail to improve due to their oligopoly on the entire process of facilitating buyer and seller payment processing.
Stripe, Block, PayPal are just mere parasites living off of other parasites (the 3-7% transaction/network/issuing bank fees).
A “rival” is a complete dissolution of these parasitic entities. Cash used to be a good alternative, but comes with its own set of setbacks that do not meet our modern era (ie, can’t pay for items with cash in e-commerce, pains of handling high amounts of cash IRL)