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
* public void testMethod() {}
 * }
 * </pre>
 * <p>
 * Note, the {@link ESIntegTestCase} uses randomized settings on a cluster and index level. For instance
 * each test might use different directory implementation for each test or will return a random client to one of the
 * nodes in the cluster for each call to {@link #client()}. Test failures might only be reproducible if the correct
 * system properties are passed to the test execution environment.
 * <p>
 * This class supports the following system properties (passed with -Dkey=value to the application)
 * <ul>
 * <li>-D{@value #TESTS_ENABLE_MOCK_MODULES} - a boolean value to enable or disable mock modules. This is
 * useful to test the system without asserting modules that to make sure they don't hide any bugs in production.</li>
 * <li> - a random seed used to initialize the index random context.
 * </ul>
 */
@LuceneTestCase.SuppressFileSystems("ExtrasFS") 
public abstract class ESIntegTestCase extends ESTestCase {
    /**
     * Property that controls whether ThirdParty Integration tests are run (not the default).
     */
    public static final String SYSPROP_THIRDPARTY = "tests.thirdparty";
    /**
     * Annotation for third-party integration tests.
     * <p>
     * These are tests the require a third-party service in order to run. They
     * may require the user to manually configure an external process (such as rabbitmq),
     * or may additionally require some external configuration (e.g. AWS credentials)
     * via the {@code tests.config} system property.
     */