I agree that 6-year-olds and other people without any production sysadmin or SRE experience are going to have a pretty bad time learning to build and deploy a Kubernetes cluster.
My point is that any professional sysadmin or SRE can learn Kubernetes just fine. Yeah, there's a lot of stuff, but there's just about as many moving parts as I expect for a system that handles what Kubernetes does. You also mostly don't have to pay complexity cost for many optional features you don't care about; you can get a minimal cluster up, and then grow it as you need more features.
I don't follow what you're saying about port 443. The kubelet API is not listening on port 443 by default. I'm as confident as I can be without checking that no kubernetes components listen on port 443 by default.
Speaking more broadly, I agree that someone with no SRE experience and no network security experience won't get much value from 30 seconds of nmap. What I was trying to say is that "accidentally exposed the kubelet API to the global internet" is something that I expect a competent sysadmin to be able to detect and notice with 30 seconds of nmap.
When I'm saying "deploying kubernetes is fine", I'm saying that anyone who has any business running nontrivial production services in a professional setting will not have any trouble learning to use and deploy Kubernetes. Deploying a cluster does require competence with sysadmin or SRE fundamentals, but not particularly more so than other systems that handle similarly-complex topics.
Also, any junior sysadmin or programmer should be able to learn to use an already-running kubernetes cluster to deploy basic services with no trouble and just a bit of time. I have trained quite a few people on this, and it really does go just fine.