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
*
     * @see #waitForRelocation()
     */
    protected final RefreshResponse refresh(String... indices) {
        waitForRelocation();
        RefreshResponse actionGet = indicesAdmin().prepareRefresh(indices)
            .setIndicesOptions(IndicesOptions.STRICT_EXPAND_OPEN_HIDDEN_FORBID_CLOSED)
            .execute()
            .actionGet();
        assertNoFailures(actionGet);
        return actionGet;
    }
    /**
     * Flushes and refreshes all indices in the cluster
     */
    protected final void flushAndRefresh(String... indices) {
        flush(indices);
        refresh(indices);
    }
    /**
     * Flush some or all indices in the cluster.
     */
    protected final FlushResponse flush(String... indices) {
        waitForRelocation();
        FlushResponse actionGet = indicesAdmin().prepareFlush(indices).execute().actionGet();
        for (DefaultShardOperationFailedException failure : actionGet.getShardFailures()) {
            assertThat("unexpected flush failure " + failure.reason(), failure.status(), equalTo(RestStatus.SERVICE_UNAVAILABLE));
        }
        return actionGet;
    }