One I ran across recently was the upgrade process for clusters. Per (https://kubernetes.io/docs/admin/cluster-management/#upgradi...) it seems that unless you're on GCE the best way to upgrade a cluster is by rebuilding it from scratch as the upgrade script is still "experimental", which doesn't seem great.
The other area that I think Kubernetes is lagging Docker quite a bit on is security documentation and tooling. There's no equivalent of the CIS guide for Docker or Docker bench, both of which are useful in understanding the security trade-offs of various configurations and choosing one that suits a given deployment.