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
* Syntactic sugar for:
     * <pre>
     *   return client().prepareIndex(index).setId(id).setSource(source).execute().actionGet();
     * </pre>
     */
    protected final DocWriteResponse index(String index, String id, XContentBuilder source) {
        return client().prepareIndex(index).setId(id).setSource(source).execute().actionGet();
    }
    /**
     * Syntactic sugar for:
     * <pre>
     *   return client().prepareIndex(index).setId(id).setSource(source).execute().actionGet();
     * </pre>
     */
    protected final DocWriteResponse indexDoc(String index, String id, Object... source) {
        return client().prepareIndex(index).setId(id).setSource(source).execute().actionGet();
    }
    /**
     * Syntactic sugar for:
     * <pre>
     *   return client().prepareIndex(index).setId(id).setSource(source).execute().actionGet();
     * </pre>
     * <p>
     * where source is a JSON String.
     */
    protected final DocWriteResponse index(String index, String id, String source) {
        return client().prepareIndex(index).setId(id).setSource(source, XContentType.JSON).execute().actionGet();
    }
    /**
     * Waits for relocations and refreshes all indices in the cluster.