Kubernetes manages containers, but what manages Kubernetes? GKE just makes the experience very painless, updates, etc.

It's better than fully self-managing it, but GKE is still less managed than I'd personally like. I just want to submit containers as jobs to be executed in "the cloud", with the cloud provider figuring out the details of where they get executed. On GKE, have to create a cluster in the cloud, then submit your jobs to your cluster, and set up logic to manage provisioning/resizing/etc., rather than just being able to submit your jobs to a giant abstracted cluster managed by Google. Joyent's Triton container service basically does that, so it's possible.

Have you tried Appengine flexible environment?