It looks like Elasticsearch is currently missing support for concurrent searching and that this is a major prospective optimization to reduce latency.

Digression: this is not the topic at hand but I personally consider the fork OpenSearch to be an historical tragedy of duplication of work and a segregation of improvements. What would be even more anti-utilitarist would be to blindly *ignore* each other advances towards making better search.

Lucene concurrent search APIs are probably among the most important feature/optimization currently not leveraged by Elasticsearch.
The fork OpenSearch has a [pull request](https://github.com/opensearch-project/OpenSearch/pull/1500) implementing support for it.

See also the [corresponding issue](https://github.com/opensearch-project/OpenSearch/issues/1286) 

I believe it would be great for end users if you could take inspiration from the PR and work on this feature.

Great blog about the Lucene feature:
https://blog.mikemccandless.com/2019/10/concurrent-query-execution-in-apache.html?m=1
See also those performance results:
https://engineeringblog.yelp.com/2021/09/nrtsearch-yelps-fast-scalable-and-cost-effective-search-engine.html
test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java
protected void ensureStableCluster(int nodeCount, @Nullable String viaNode) {
        ensureStableCluster(nodeCount, TimeValue.timeValueSeconds(30), false, viaNode);
    }
    protected void ensureStableCluster(int nodeCount, TimeValue timeValue, boolean local, @Nullable String viaNode) {
        if (viaNode == null) {
            viaNode = randomFrom(internalCluster().getNodeNames());
        }
        logger.debug("ensuring cluster is stable with [{}] nodes. access node: [{}]. timeout: [{}]", nodeCount, viaNode, timeValue);
        ClusterHealthResponse clusterHealthResponse = client(viaNode).admin()
            .cluster()
            .prepareHealth()
            .setWaitForEvents(Priority.LANGUID)
            .setWaitForNodes(Integer.toString(nodeCount))
            .setTimeout(timeValue)
            .setLocal(local)
            .setWaitForNoRelocatingShards(true)
            .get();
        if (clusterHealthResponse.isTimedOut()) {
            ClusterStateResponse stateResponse = client(viaNode).admin().cluster().prepareState().get();
            fail(
                "failed to reach a stable cluster of ["
                    + nodeCount
                    + "] nodes. Tried via ["
                    + viaNode
                    + "]. last cluster state:\n"
                    + stateResponse.getState()
            );
        }
        assertThat(clusterHealthResponse.isTimedOut(), is(false));
        ensureFullyConnectedCluster();