That's right. Using cryptocurrency is one thing, and staying anonymous while using cryptocurrency is another. The ordinary criminals may jump in to use Bitcoin or Monero. But he may not be able to convert these cryptocurrencies to fiat or other physical assets. And he may not be able to keep his cryptocurrency transactions secure (i.e without any links that can be traced back).
Unless they use mixer which is a favorite thing to them. But yeah, I agree because most criminals prefer using fiat because banks can cover for them and they can use this dirty money to buy assets that will clean their money.
Finding a reliable cryptocurrency mixer is getting difficult nowadays. A number of them have been closed down by the authorities in the recent times. The most well known example is that of Bestmixer.io. It was taken down in 2018, by a combined team led by the Europol. Some of the other mixing services proved to be exit scams, while some others were having phishing links.