by the way Adrian my English might be off but reading your own docs they are confusing
https://rancher.com/docs/rancher/v2.x/en/installation/k8s-install/
they explictly say "it is better to install Rancher on a single-node Kubernetes cluster than to install it with Docker"
which implies it is possible to install it in the same cluster you use for workloads and it is also possible to install it in docker
do I understand wrong?