The core idea isn’t pods. The core idea is reconciliation loops: you have some desired state - a picture of how you’d like a resource to look or be - and little controller loops that indefinitely compare that to the world, and update the world.
Much of the complexity then comes from the enormous amount of resource types - including all the custom ones. But the basic idea is really pretty small.
I find terraform much more confusing - there’s a spec, and the real world.. and then an opaque blob of something I don’t understand that terraform sticks in S3 or your file system and then.. presumably something similar to a one-shot reconciler that wires that all together each time you plan and apply?
To me the core of k8s is pod scheduling on nodes, networking ingress (e.g. nodeport service), networking between pods (everything addressable directly), and colocated containers inside pods.
Declarative reconciliation is (very) nice but not irreplaceable (and actually not mandatory, e.g. kubectl run xyz)
You can invent a new resource type that spawns raw processes if you like, and then use k8s without pods or nodes, but if you take away the reconciliation system then k8s is just an idle etcd instance
Imagine if pods couldn't reach other and you had to specify all networks and networking rules.
Or imagine that once you created a container you had to manually schedule it on a node. And when the node or pod crashes you have to manually schedule it somewhere else.