This is true. But mastercard facilitates the liquidation of this credit via their payment systems, which people will continue to use. Initially people will likely use ether as a store of value/hedge against the traditional economy. Also dapp fuel, as we all hope.

Furthermore, take a look at coinbase as an example of a company profiting heavily on this new payment system. Mastercard has an opportunity to capture some of the new value being created in the ecosystem. They don't have to fall off the map if we all start using ether. If they do, they failed to innovate. I suspect their execs understand this.