You're saying they're imposters but I wouldn't say mixers are scams or say they're imposters of coinjoin services. They're providing a service which isn't coinjoin it's different obfuscating in different ways. Coinjoin's the best way to mix but it doesn't mean mixers aren't offering a service.
Mixers are scams that are imposters of coinjoin services. They do not provide any privacy, they simply allow the operator to steal your coins.
If it's a basic swap from Bitcoins to Monero it's going to add a layer of privacy first hand so if it's mixing more it's still going to work if they don't record data trails.