Are you assuming the workloads have to use K8s APIs? Where is this coming from? If that’s not the case can you actually explain with a concrete example?
https://helm.sh/docs/topics/version_skew/
Istio: https://istio.io/latest/docs/releases/supported-releases/#su...
Literally every kubernetes manifest that hits the server uses a k8s api:
apiVersion: apps/v1(genuine tone, not rhetorical)
But, to reiterate, everything uses APIs. The *betavX APIs are of course likely to be deprecated and replaced with stable APIs after a few versions.
So if you are going to compare with a managed solution, compare with something equivalent. Take a bare managed cluster and add a single Deployment to it, it will be no more complex than ECS, while giving you much better developer ergonomics.