> Kubernetes is a component (like containerd or swarmkit)

That's a bit of stretch. Everything that people use to build something bigger is a "component", but that doesn't make it not a platform.

Kubernetes is absolutely a platform, in that it is the base layer on which higher-level systems are built. It's somewhat less opinionated than OpenShift (which is literally Kubernetes++) or Docker (the full stack), but that is by design. Opinions are too fickle - Kubernetes is here to service the evolving fashion of opinions, while providing durable base abstractions.