You are correct that there is no benefit to consumers in saving retailers money. Additionally, Visa can terminate a Retailers account if they provide a discount

You are correct that there is no benefit to consumers in saving retailers money. Additionally, Visa can terminate a Retailers account if they provide a discount for using an alternative payment system. This may not be in all markets in the market it exist in, it also may not be legal. You are 100% correct regarding Ethereum gas fees. Transaction fees on current generation L1s are 0.0025 cents.