Just a small data point:

I’ve personally never seen DCC offered at mainstream banks in Hong Kong before.

Today at a Bank of China ATM in Mongkok I was offered 7.5560 HKD per US dollar, rather than the true rate of 7.8408 per dollar, a 3.8% markup.

I used my Capital One 360 card so there were no foreign transaction or foreign ATM fees. I generally use my Schwab visa debit card, and it’s possible that DCC has always been offered on debit mastercards and this is just my first experience using one - not sure.