We (https://www.ReactiveOps.com) run a lot of clusters for our clients in AWS (and also GKE, but..) using kops. It's definitely possible to run a lot of clusters, but kops is only one piece of the puzzle. Autoscaling, self-healing, monitoring and alerting, cluster logging, etc. is all other things you have to deal with, which are non-trivial (they scale workload per cluster, so...)

We open sourced our kube generator code, called pentagon, which uses kops, terraform https://github.com/reactiveops/pentagon