If there is a signature waiver or device verified transaction, how would you be able to contest the transaction to voice your dissent? It would be the merchant's word against yours.

At least with a signature receipt you can refuse to sign or deface the "I have been offered a choice of..." wording and write DCC REFUSED! before taking a photo and signing.

There are reports that the Pays successfully dodge DCC but a contactless transaction with a card supporting contactless is still susceptible to DCC. I used Android Pay fairly liberally in Italy along with my CSR and didn't see any DCC, including at the duty free at FCO. For hotels, I used the SPG AmEx, so there wasn't DCC. I tried - and was denied - at Fortnum & Mason LHR that trip the opportunity to use Android Pay, so I couldn't see if I could bypass DCC.