That you are getting a kickback does not mean they aren’t extracting monopoly rent. The rents, and your kickback, is in fact supported by slightly higher prices, which for you will roughly cancel out, but which are paid in full by people not using credit cards.

One can certainly argue that this system is net positive due, e.g., to greater credit availability for people who need it, chargeback discipline, etc. It’s a very complicated system that impacts a bunch of stuff. But it being merely a ~3% surcharge (on most retail transactions nationwide!) does not deflect the monopoly charge.