If you start using more esoteric features the reliability of k8s goes down. Guess what happens when you enable the in place vertical pod scaling feature gate?

It restarts every single container in the cluster at the same time: https://github.com/kubernetes/kubernetes/issues/122028

We have also found data races in the statefulset controller which only occurs when you have thousands of statefulsets.

Overall, if you stay on the beaten path k8s reliability is good.