So in short, it is very easy to do anonymous transfer by depositing funds on exchange and withdrawing to other addresses. Why to pay 1-3% fees on Mixers when it could be done for much less on Exchanges. Exchanges like Binance charge just 0.0005 BTC to process withdrawals.
You have a point in your argument, but exchanges require kyc which means that people can use exchanges only if they have funds from honest places. A criminal will not take stolen funds to exchange, he will take stolen funds to mixers, which is why I believe that in a few years governments will pursue the mixers more severely and I believe the punishment for executing a mixer may be as severe as possible. Note that most exchanges and even online casinos are asking people to do KYC and it won't be long before the wallets also make people do KYC