Most autoscaling functionality is implemented on top of the upstream cluster-autoscaler component, and GKE documentation claims to remove nodes when pods fit onto other nodes as well[1], so it does have the same "defragging" functionality. It might not be configured aggressive enough for their liking though (but even then, GKE has a more aggressive autoscaling profile that might do the trick).

My point is that while the original post is reporting problems with autoscaling in Kubernetes without enough details to go by, cluster-autoscaler is fairly good at its job of downsizing clusters if you take the time to a) optimize its configuration and b) make sure your workloads are configured in a way that allows downsizing clusters.

[1] https://cloud.google.com/kubernetes-engine/docs/concepts/clu...