That's not correct. Virtio devices have different security properties and many of them expose the host system to considerable risks. Using containerization on the host is one way to limit the latter. See e.g. https://github.com/libkrun/libkrun/#security-model for more details.
> That runs the codex OCI in a qemu microvm.
AFAIU it's actually the other way around: krun spawns a libkrun-based (not QEMU-based) VM inside a crun container. Source: https://github.com/libkrun/libkrun/discussions/538#discussio...
So with your solution you get the additional security benefit of containerizing the hypervisor on the host.