I am not so sure about this. The merchant fees for card payments in the EU are regulated. They are capped at max. 0.3 %. But not for cards issued outside of the scope of the EU, obviously. Even after Revolut is becoming available in the US, merchant fees for US issued cards will still be higher.
There is a possibility of course that Revolut will waive these fees once they are issuing US cards as well (it would be cost neutral for them), but since they are also offering USD accounts for customers that use UK/EU issued cards … there are many details to consider.