You're right technically, but who writes a controller that does nothing? Also, just the existence of the CRD can be enough to signal state to other controllers,

You're right technically, but who writes a controller that does nothing? Also, just the existence of the CRD can be enough to signal state to other controllers, so there are some knock-on benefits to just having it there in storage. Regardless of corner cases, this is a step change difference between tools like terraform/pulumi that reach out and call APIs and finish executing compared to k8s which supports reconciliation. A tool with reconciliation is strictly more capable than one without (for better or for worse).