You don't have to use docker pull. You can use any system capable of distributing a standard OCI bundle, including (but not limited to) docker.

runc doesnt use docker format containers, you just provide a filesystem. You can store your containers for runc by curling a tarfile if you like.

That isn't adequate. The reason LXC languished and Docker took off is because of immutable images, layers, Dockerfiles, and push/pull. If OCI has none of those then it is pointless.