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/ESSingleNodeTestCase.java
logger.debug("indices {} are green", indices.length == 0 ? "[_all]" : indices);
        return actionGet.getStatus();
    }
    @Override
    protected NamedXContentRegistry xContentRegistry() {
        return getInstanceFromNode(NamedXContentRegistry.class);
    }
    protected boolean forbidPrivateIndexSettings() {
        return true;
    }
    /**
     * waits until all shard initialization is completed.
     *
     * inspired by {@link ESRestTestCase}
     */
    protected void ensureNoInitializingShards() {
        ClusterHealthResponse actionGet = clusterAdmin().health(new ClusterHealthRequest("_all").waitForNoInitializingShards(true))
            .actionGet();
        assertFalse("timed out waiting for shards to initialize", actionGet.isTimedOut());
    }
    /**
     * Whether we'd like to enable inter-segment search concurrency and increase the likelihood of leveraging it, by creating multiple
     * slices with a low amount of documents in them, which would not be allowed in production.
     * Default is true, can be disabled if it causes problems in specific tests.
     */
    protected boolean enableConcurrentSearch() {
        return true;
    }
}