> That seems to imply that there are no grey or black markets for currencies. This is contrary to what has been observed in history and in some countries today.

Grey and black market currencies exist but the exchange rate is very painful. Its mostly only viable when the fiat currency is unstable (or in the black market) for that reason.

Either way, its largely useless in the country it has been grey/black market'd and they are relying on their ability to convert it elsewhere.

That doesn't negate the damage though. Requiring a grey or black market to use the currency in a nation of economic significance restricts bitcoin's utility. This will be a value hit when competing against any potential currency that can overcome those hurdles.

localbitcoins was a thing long before you could use exchanges in lots of countries.