I would agree that contactless does seem to avoid a DCC prompt in most cases. I am unsure if it is by design or the folks that design the DCC software have not gotten around to updating the software flow yet.

Yes, I did find one major retailer in the UK that still forced the DCC prompt on tap transactions. It was about 3-5% above the wholesale rate and did seem unique. It was not difficult to opt-out, but it definitely is possible to get the prompt even with a NFC tap.