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
import static org.hamcrest.Matchers.startsWith;
/**
 * {@link ESIntegTestCase} is an abstract base class to run integration
 * tests against a JVM private Elasticsearch Cluster. The test class supports 2 different
 * cluster scopes.
 * <ul>
 * <li>{@link Scope#TEST} - uses a new cluster for each individual test method.</li>
 * <li>{@link Scope#SUITE} - uses a cluster shared across all test methods in the same suite</li>
 * </ul>
 * <p>
 * The most common test scope is {@link Scope#SUITE} which shares a cluster per test suite.
 * <p>
 * If the test methods need specific node settings or change persistent and/or transient cluster settings {@link Scope#TEST}
 * should be used. To configure a scope for the test cluster the {@link ClusterScope} annotation
 * should be used, here is an example:
 * <pre>
 *
 * {@literal @}NodeScope(scope=Scope.TEST) public class SomeIT extends ESIntegTestCase {
 * public void testMethod() {}
 * }
 * </pre>
 * <p>
 * If no {@link ClusterScope} annotation is present on an integration test the default scope is {@link Scope#SUITE}
 * <p>
 * A test cluster creates a set of nodes in the background before the test starts. The number of nodes in the cluster is
 * determined at random and can change across tests. The {@link ClusterScope} allows configuring the initial number of nodes
 * that are created before the tests start.
 *  <pre>
 * {@literal @}NodeScope(scope=Scope.SUITE, numDataNodes=3)
 * public class SomeIT extends ESIntegTestCase {