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
* Note we create these test class instance via reflection
         * since JUnit creates a new instance per test and that is also
         * the reason why INSTANCE is static since this entire method
         * must be executed in a static context.
         */
        assert INSTANCE == null;
        if (isSuiteScopedTest(targetClass)) {
            
            INSTANCE = (ESIntegTestCase) targetClass.getConstructor().newInstance();
            boolean success = false;
            try {
                INSTANCE.printTestMessage("setup");
                INSTANCE.beforeInternal();
                INSTANCE.setupSuiteScopeCluster();
                success = true;
            } finally {
                if (success == false) {
                    afterClass();
                }
            }
        } else {
            INSTANCE = null;
        }
    }
    /**
     * Compute a routing key that will route documents to the <code>shard</code>-th shard
     * of the provided index.
     */
    protected String routingKeyForShard(String index, int shard) {
        return internalCluster().routingKeyForShard(resolveIndex(index), shard, random());