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
}
    @Override
    protected NamedXContentRegistry xContentRegistry() {
        if (isInternalCluster() && cluster().size() > 0) {
            
            return internalCluster().getInstance(NamedXContentRegistry.class);
        } else {
            
            return new NamedXContentRegistry(ClusterModule.getNamedXWriteables());
        }
    }
    protected boolean forbidPrivateIndexSettings() {
        return true;
    }
    /**
     * Override to return true in tests that cannot handle multiple data paths.
     */
    protected boolean forceSingleDataPath() {
        return false;
    }
    /**
     * Returns an instance of {@link RestClient} pointing to the current test cluster.
     * Creates a new client if the method is invoked for the first time in the context of the current test scope.
     * The returned client gets automatically closed when needed, it shouldn't be closed as part of tests otherwise
     * it cannot be reused by other tests anymore.
     */
    protected static synchronized RestClient getRestClient() {
        if (restClient == null) {
            restClient = createRestClient();
        }