Swarm is used but I have heard many companies migrating from swarm to k8s and openshift. Swarm is just unstable, network connectivity is flaky, not sure how can you run it in prod (maybe you can't?).
As for k8s - would recommend it for anything from hobby projects to large prod deployment. Easy to set up anywhere.
This article is indeed very shallow and clearly author hasn't bothered to do some research.