The lions share is going back to whoever issued you a credit card. If its say an airline card, that'd be rewards 2 which ranges from 1.65% + $0.10 per transaction all the way up to 2.7% + $0.10. Then you add on network & platform fees (0.1% + $0.06 per transaction) and whatever minuscule profit margin your ISO/MSP can get and your at 1.5% to 2% on average.
Rarely will a business get the 2.3% rate, that is purely a temporary promotion for supermarkets that are new to American Express. Also, Amex acts as the bank, with the same rewards programs and incentives to retain customers.
Visa Interchange Rates: https://usa.visa.com/dam/VCOM/global/support-legal/documents...