> Thinking of Kubernetes as a runtime for declarative infrastructure instead of a mere orchestrator results in very practical approaches to operate your cluster.

This is a pretty good definition.

I think part of the challenge is the evolution of K8s over time sometimes makes it feel less like a coherent runtime and more like a pile of glue amalgamated from several different components all stuck together. That and you will have to be aware of how those abstractions stick together with the abstractions from your cloud provider, etc...