You can also spin up Tomcat with everything needed to run an application with your local package manager and you can deploy your WAR file by putting it in the right location, but that's not what IBM, Oracle, and Red Hat have sold as Application Servers.

This is effectively what is being sold now but using Kubernetes and Containers instead of Application Servers and J2EE

The difference is that Tomcat can’t run arbitrary badly-behaved third-party x86 binaries under itself. (I mean, it can, but it doesn’t have the facilities to protect itself from them.)

K8s lets you build “containers” out of whatever existing software happens to be laying around, rather than having to write your services from the ground up for being run in a container.

Easy peasy.

Now try troubleshooting it.

On the cloud providers it is fully managed so nothing really to troubleshoot from the core platform perspective. The applications e.g. ingress will likely do but that's the same as if you were running on bare metal without Kubernetes.

And again the monitoring and auditing on Kubernetes is significantly better than trying to roll your own. There is detailed logs and metrics up and down the stack.

"On the cloud providers it is fully managed so nothing really to troubleshoot"

Clearly, you haven't run much at scale or experienced many problems.

Troubleshoot a network issue through an ingress, kube-proxy and then down to the pod.

Troubleshoot an issue with kube-api or etcd when you have no access to either the master or the etcd cluster.

Troubleshoot a load issue on a node related to IO.