No: I was wrong to compare my case to dddscy's and have gone back and edited my post. In my case I checked the TWD box manually (and told my server that I was doing so), but did not receive a fresh customer copy. (The 'draft' receipt included the phrase "no signature required".)
I won't "name and shame" the restaurant: dinner was wonderful and I am not accusing them of deliberately attempting to rip us off. It seems more likely that the cashier made a mistake (or was on autopilot and selected the option most often chosen by foreigners?).
But that's what DCC is, it is them attempting to rip you off. We have articulated there is no common case where it is advantageous for the cardholder to be DCCed. Them refusing your preference on the quote slip is also nothing else if not a deliberate attempt to rip you off (if they really cared about settling the transactions in cardholder currency, they would have.)
Obviously, nobody can force you to name the restaurant, but I think that you are giving them too much credit. DCC doesn't just accidentally happen, it is something that the restaurant management chose to sign up for and chose not to adequately train their personnel to deal with.