Containers are isolated but a far, far cry from maximally isolated. They’re still sharing a Linux Kernel with some hand waving and cgroups. The network isolation and QoS side is half-baked even in the most mature implementations.

HVM hypervisors were doing stronger, safer, better isolation than Docker was 10 years ago. They are certainly no-thinking required though which leads to the abysmal state of containerized security and performance we have currently.