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
*/
    protected final void enableAllocation(String... indices) {
        updateIndexSettings(
            Settings.builder().put(EnableAllocationDecider.INDEX_ROUTING_ALLOCATION_ENABLE_SETTING.getKey(), "all"),
            indices
        );
    }
    /**
     * Syntactic sugar for disabling allocation for <code>indices</code>
     */
    protected final void disableAllocation(String... indices) {
        updateIndexSettings(
            Settings.builder().put(EnableAllocationDecider.INDEX_ROUTING_ALLOCATION_ENABLE_SETTING.getKey(), "none"),
            indices
        );
    }
    /**
     * Returns a random admin client. This client can be pointing to any of the nodes in the cluster.
     */
    protected static AdminClient admin() {
        return client().admin();
    }
    /**
     * Returns a random cluster admin client. This client can be pointing to any of the nodes in the cluster.
     */
    protected static ClusterAdminClient clusterAdmin() {
        return admin().cluster();
    }
    /**
     * Returns a random indices admin client. This client can be pointing to any of the nodes in the cluster.