That's not how pseudonymity works, you are anonymous until you accidentally leak, or have to leak, PII linked to your wallet. They can be totally anonymous right now without any mixing. Once they need to convert to fiat they may have to mix first. Or maybe exchange cash wearing a mask with a stranger on the street in a foreign country, etc. Pseudonymity doesn't mean you're not anonymous until you mix.
Do you have more information about how susceptible CoinJoin is, because what I've seen for someone that knows what they are doing it would be near impossible, especially if they then convert it to Monero after.
