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
/**
     * Waits for all relocations and force merge all indices in the cluster to 1 segment.
     */
    protected ForceMergeResponse forceMerge() {
        waitForRelocation();
        ForceMergeResponse actionGet = indicesAdmin().prepareForceMerge().setMaxNumSegments(1).execute().actionGet();
        assertNoFailures(actionGet);
        return actionGet;
    }
    /**
     * Returns <code>true</code> iff the given index exists otherwise <code>false</code>
     */
    protected static boolean indexExists(String index) {
        return indexExists(index, client());
    }
    /**
     * Returns <code>true</code> iff the given index exists otherwise <code>false</code>
     */
    public static boolean indexExists(String index, Client client) {
        GetIndexResponse getIndexResponse = client.admin()
            .indices()
            .prepareGetIndex()
            .setIndices(index)
            .setIndicesOptions(IndicesOptions.LENIENT_EXPAND_OPEN_CLOSED)
            .execute()
            .actionGet();
        return getIndexResponse.getIndices().length > 0;
    }
    /**
     * Syntactic sugar for enabling allocation for <code>indices</code>