I don't see a way in which mixers can have it easier since, they use same network as the rest of the bitcoin community. Compounding coins comes with mo advantage as, the number of confirmations would play a role too.
In other words, you want a mixer to work like an exchange, whereby the compound transaction in order to save fees?
You do realize this can make the job easier for Chainalysis companies and anyone trying to snoop people's transactions with all the co-spending happening in a certain pattern. I am not expert in different mixing techniques, but I think this can mess up privacy.