While I've generally managed to avoid these disputes by either being careful (outside of China) or paying cash (in China), when I have disputed with CC company they've been oddly ill-equipped to dispute only a portion of the charge on a DCC. One time they eventually credited back the difference; another time (for a small purchase - <$25) they just ate the charge.

Regardless, I think it's useful to call the problem to their attention - even if they decide it's not worth the effort so they write off, I imagine they keep track of write-offs and notice patterns like "a lot of DCC-based writeoffs in China"