In theory, wouldn't make sense to run all the code that runs as the root user as ring zero? The root user still can access read/write the whole memory of the s

In theory, wouldn't make sense to run all the code that runs as the root user as ring zero? The root user still can access read/write the whole memory of the system anyway via /dev/mem, load kernel modules, and do practically anything on the system. In that context, a change of privilege is useless in practice, and can lead to performance degradation. This will lead performance benefits in most system daemons, notably programs that interact closely with the kernel like systemd.