a country that wants to avoid sanctions in this way benefit from using Bitcoin.
Countries can not and do not use bitcoin to avoid sanctions.
Debatable because any entity can use Bitcoin to settle the payment side of things.
It's a pretty simple matter, if country A is sanctioned by country B then country A can not use any means of payment including bitcoin to trade with country B or any country following B. And if country A and C don't give a shit about sanctions they will trade with each other with or without bitcoin.
The point of Bitcoin is the country that sanctioned "country A" can't censor any entity that decides to send, receive, or settle payments through Bitcoin.
Keep in mind that bitcoin has the most transparent ledger in the world. So for example if country D was worried a little about getting sanctioned because of trading with country A, it would never use bitcoin!
There are limitations, but there are solutions. Plus "taint" doesn't exist in the blockchain. It doesn't make Bitcoin less censorship-resistant.
Bitcoin is just another way to dump US dollar as reserve currency and for trades. Sanctions only give the incentive to do it faster.
As I said earlier, other means of payment are already being used (a LOT more than bitcoin will be). Even Saudis are talking about dumping US dollar and using Yuan for oil exports!
Yuan is an alternative, Bitcoin is another alternative. Any entity is free to choose.