I do think their is debate as to if namespace containers are more or less secure the kvm and qemu VM's, I think the surface area of kvm and qemu is still very large and difficult to reason about. I think on some cpu architectures virtualization can be implemented on easy then x86 or x86_64, I think I read how risc-v have a much simpler and easy to work with virtualization instructions.

The surface area of the virtio driver should not be underestimated either I think.

Virtualization instructions are the easy part. x86 does have a need for yuckier instruction emulation than other architectures, but the really complex part where you find vulnerabilities is page table management which is only optimized to the extreme on x86 but, in reality, it has very similar needs across architectures.