It is a win friction-wise. I am pretty sure Visa/Mastercard have negligible costs when processing a transaction, and that 3% is what I guess they think is the upper boundary of what merchants are willing to pay before there's an incentive for a competitor with lower fees to appear.

Visa/Mastercard are a duopoly, which means they can extract rents.

Yes, I’m willing to pay $100 for a liter of water if you’re the only one selling it. I get a lot of value out of it!

In a competitive market, competition eventually drives down prices to a price that somewhat approaches the cost of providing the service.

This isn’t happening in payment, due to insurmountable network effects.