> But then here you are saying your team "operates a couple thousand" clusters. If 50 is far too many, and bound to be unmanageable, how is it reasonable to have more than a thousand?

It's not unmanageable to have a couple thousand Kube clusters but you need to have the resources to build a staff and tool chain to support that, which most companies cannot do.

Clusters are how we shard our customer workloads (a workload being say a dozen services and a database, a customer may have many workloads spread across the entire fleet). We put between 100 and 150 workloads per cluster. What this gives us is a relatively small impact area if a single cluster becomes problematic as it only impacts the workloads on it.