I think scale has less to do with how many customers you're serving and more to do with how much data you're processing. Streaming video to 10,000 people is much more data-intensive than exposing a CRUD interface to 1M.
Also k8s is not, in and of itself, a complication. You're going to have to worry about the same set of problems whether or not you use k8s. Deployments, load-balancing, self-healing, etc. It's not like ops teams didn't do anything before k8s came along.