MacOS apps are designed to be self contained and not require isolation, unlike most Linux distros, which are designed to use FHS and share their state/dependencies with everything else on the system.

Further you can sandbox processes just fine on MacOS without needing to mock the whole userspace, like you do on Linux. This will give you the same degree of isolation that a container does.

Neither is using macfuse as a stand in for overlayfs and bind mounts.

My point is "as fast as it gets" is using MacOS how MacOS is designed: ie, through sandboxing and not containerization that pretends the MacOS userspace is Linux. It's not Linux.

There is a fundamental trade off between isolation and performance. You cannot securely share resources without overhead.