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
nodePlugins(),
            getClientWrapper(),
            clusterName,
            transportAddresses
        );
    }
    protected Settings externalClusterClientSettings() {
        return Settings.EMPTY;
    }
    protected boolean ignoreExternalCluster() {
        return false;
    }
    protected TestCluster buildTestCluster(Scope scope, long seed) throws IOException {
        String clusterAddresses = System.getProperty(TESTS_CLUSTER);
        if (Strings.hasLength(clusterAddresses) && ignoreExternalCluster() == false) {
            if (scope == Scope.TEST) {
                throw new IllegalArgumentException("Cannot run TEST scope test with " + TESTS_CLUSTER);
            }
            String clusterName = System.getProperty(TESTS_CLUSTER_NAME);
            if (Strings.isNullOrEmpty(clusterName)) {
                throw new IllegalArgumentException("External test cluster name must be provided");
            }
            return buildExternalCluster(clusterAddresses, clusterName);
        }
        final String nodePrefix = switch (scope) {
            case TEST -> TEST_CLUSTER_NODE_PREFIX;
            case SUITE -> SUITE_CLUSTER_NODE_PREFIX;
        };
        boolean supportsDedicatedMasters = getSupportsDedicatedMasters();
        int numDataNodes = getNumDataNodes();