The only datapoint I can give is that moving from AWS to GCP reduced our bill by 2/3rds. That isn't a 1 to 1 comparison though as we did a re-platforming at the same time.

Moving from AWS ECS to GCP Kubernetes was probably the biggest money saver. It reduced the amount of compute needed by a huge amount. Being able to safely use pre-emptive VMs in Kubernetes is also leads to huge savings.

I am sure that if we used Kubernetes in AWS it would have had a similar cost reduction.