For large scale you have to first make your application capable of scaling. That's a bit that's missing from most of these conversations. Only the simplest programs can "scale up" by just adding more programs - most have to be re-architected to move all the state in the program to some other service.

That is to say, if scaling is your primary concern, you have a dozen other things more important to fix than your choice to use shell scripts vs. Kubernetes.

And, fwiw, Linux has run professional services somewhere around 10x longer on those "beginner tools" than containers have even existed.