RonDB uses a non-blocking 2PC algorithm - commits in memory, and then does a group commit of transactions to disk every 500ms. This means it can handle insane write throughput, as well as read throughput. However, if both your DB nodes fail, you could lose 500ms of data - which is not the end of the world for k8s. Normally, you would locate DB nodes in different AZes, reducing the probabilty of correlated failures.
At that point it is apples to oranges. One of the main reasons why etcd writes are slow is because they are guaranteed to be durably persisted across the quorum.
If you just turned off file system syncs in etcd you could probably get an order of magnitude better performance as well.
