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
}
    /**
     * Waits until all nodes have no pending tasks.
     */
    public void waitNoPendingTasksOnAll() throws Exception {
        assertNoTimeout(clusterAdmin().prepareHealth().setWaitForEvents(Priority.LANGUID).get());
        assertBusy(() -> {
            for (Client client : clients()) {
                ClusterHealthResponse clusterHealth = client.admin().cluster().prepareHealth().setLocal(true).get();
                assertThat("client " + client + " still has in flight fetch", clusterHealth.getNumberOfInFlightFetch(), equalTo(0));
                PendingClusterTasksResponse pendingTasks = client.admin().cluster().preparePendingClusterTasks().setLocal(true).get();
                assertThat(
                    "client " + client + " still has pending tasks " + pendingTasks,
                    pendingTasks.pendingTasks(),
                    Matchers.emptyIterable()
                );
                clusterHealth = client.admin().cluster().prepareHealth().setLocal(true).get();
                assertThat("client " + client + " still has in flight fetch", clusterHealth.getNumberOfInFlightFetch(), equalTo(0));
            }
        });
        assertNoTimeout(clusterAdmin().prepareHealth().setWaitForEvents(Priority.LANGUID).get());
    }
    
    public void assertResultsAndLogOnFailure(long expectedResults, SearchResponse searchResponse) {
        final TotalHits totalHits = searchResponse.getHits().getTotalHits();
        if (totalHits.value != expectedResults || totalHits.relation != TotalHits.Relation.EQUAL_TO) {
            StringBuilder sb = new StringBuilder("search result contains [");
            String value = Long.toString(totalHits.value) + (totalHits.relation == TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO ? "+" : "");
            sb.append(value).append("] results. expected [").append(expectedResults).append("]");
            String failMsg = sb.toString();