Kine (https://github.com/k3s-io/kine) is a shim or an external process (when not k3s) that translates the etcd api to enable compatibility with a database or alternative data store. Kubernetes natively talks etcd, so this translation is what enables its usage with sqlite or another database, but it incurs an overhead.

I don't have specific numbers unfortunately since it was years ago I benchmarked Kine against etcd. But I had a better results with etcd both in cluster and single node.

I happened to stumble upon this paper that echos my experience. https://programming-group.com/assets/pdf/papers/2023_Lightwe... Particularly, the high controller cpu usage (even for an empty cluster), and higher latencies.