To me, it looks like the ChipMixer operators have run it quite competently
I'm not so sure, because if the feds didn't break into Mihn's place, then he likely didn't have the control in the first place. I read it was hosted on DigitalOcean, whose reputation I'm not aware of, but I'm aware it's a middleman. The best course of a mixer is to run it on some machine you possess, and to obfuscate your location, use Tor.
I think that ChipMixer's biggest mistake was to not go fully anonymous from the beginning.
As for the 7 TB: we know absolutely nothing of what ChipMixer held there, besides private keys (which if I remember correctly were supposed to be deleted). The only thing I remember they were highlighting is that they delete is logs.