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
restClient.close();
            restClient = null;
        }
        assertBusy(() -> {
            int numChannels = RestCancellableNodeClient.getNumChannels();
            assertEquals(
                numChannels
                    + " channels still being tracked in "
                    + RestCancellableNodeClient.class.getSimpleName()
                    + " while there should be none",
                0,
                numChannels
            );
        });
    }
    private void afterInternal(boolean afterClass) throws Exception {
        boolean success = false;
        try {
            final Scope currentClusterScope = getCurrentClusterScope();
            if (isInternalCluster()) {
                internalCluster().clearDisruptionScheme();
            }
            try {
                if (cluster() != null) {
                    if (currentClusterScope != Scope.TEST) {
                        Metadata metadata = clusterAdmin().prepareState().execute().actionGet().getState().getMetadata();
                        final Set<String> persistentKeys = new HashSet<>(metadata.persistentSettings().keySet());
                        assertThat("test leaves persistent cluster metadata behind", persistentKeys, empty());
                        final Set<String> transientKeys = new HashSet<>(metadata.transientSettings().keySet());
                        assertThat("test leaves transient cluster metadata behind", transientKeys, empty());