There are quite a few things that I had to leave out as the post was getting really long. I am writing a follow up article now titled "How Kubernetes and twelve-factor methodology saved us USD 300k in 24 months" where I am going to touch on this.
The short version is that we never intended to stay with a cloud provider due to the costs of operating a large cluster (we continue to use GCP for critical components of our infrastructure, such as monitoring and alerting). It was convenient while we could afford it thanks to their startup programs, but migrating our data aggregation workers from cloud providers to dedicated servers cut costs by 40% (which adds up to a lot, as we are using ±0.5k vCPUs and _a lot_ of RAM).
Maybe I missed it.