I don’t really understand your argument.
I’d suggest most Curve customers wouldn’t be paying fees to Creation even if Curve didn’t exist, because if they’re sensible enough to use Curve they’re sensible enough to find a different credit card that doesn’t charge forex fees…they’re not exactly difficult to find!
Creation are a tiny card provider. They only advertise one product to new customers now… I’d be surprised if any of the big players were really that fussed - they still get their interchange/transaction fees and interest which I imagine is the bulk of their income. The big banks get to charge the merchant bank fees on the retailer side too, so any payment by card is a win for them whoever’s card it is.