We found that the savings from switching from VMs in ASGs to k8s never really materialized. OS overhead wasn't actually that much and once you're requesting cpu / memory you can't fit as many pods per host as you think.

Plus you're competing with hypervisors for maxing out hardware which is rock solid stable.

My experience was quite the opposite, but it depends very much on the workload.

That is, I didn't say the competition was between AWS ASGs and k8s running on EC2, but having already a certain amount of capacity that you want to max out in flexible ways.