I'm going to stand by what I said: it was a bad practice from the side of ChipMixer, but it's not a flaw in the concept of centralized mixers, in itself.
If a service does everything correctly (including deleting private keys and any backups of them after handing them to the user), something like what happened to CM could simply not happen.
If you are okay with sacrificing ownership to custodians, why don't you at least recommend a custodian that can't track their users, like ecash mints or a federated chain with CT enabled? Why is it so commonplace to see people recommending "mixer sites" that gain complete access to your financial history in addition to ownership of the actual funds?