No, the assertion that nginx on ubuntu is equivalent to kubernetes os mind-numbingly wrong, for starters for being entirely and completely oblivious to containers. The comparison isn't even wrong: it simply makes no sense at all.

And no, being able to run software is not equivalent to Kubernetes. It's not even in the same ballpark of the discussion. You are entirely free to go full Amish on your pet projects but let's not pretend that managing a pet server brings any operational advantage over, say, just being able to seamlessly deploy N versions of your app with out-of-the-box support for blue/green deployments and with the help of a fully versioned system that allows to undo and resume operating with a past configuration. You don't do that by flaunting iptables and yum, do you?

If anyone needs to operate a cluster then they need tooling to manage and operate a cluster. Your iptables script isn't it.