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
int numberOfShards = numberOfShards();
        if (numberOfShards > 0) {
            builder.put(SETTING_NUMBER_OF_SHARDS, numberOfShards);
        }
        int numberOfReplicas = numberOfReplicas();
        if (numberOfReplicas >= 0) {
            builder.put(SETTING_NUMBER_OF_REPLICAS, numberOfReplicas);
        }
        
        if (randomInt(9) < 3) {
            final String dataPath = randomAlphaOfLength(10);
            logger.info("using custom data_path for index: [{}]", dataPath);
            builder.put(IndexMetadata.SETTING_DATA_PATH, dataPath);
        }
        
        builder.put(UnassignedInfo.INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING.getKey(), 0);
        if (randomBoolean()) {
            builder.put(IndexSettings.INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING.getKey(), between(0, 1000));
        }
        if (randomBoolean()) {
            builder.put(
                INDEX_SOFT_DELETES_RETENTION_LEASE_PERIOD_SETTING.getKey(),
                timeValueMillis(
                    randomLongBetween(
                        0,
                        randomBoolean() ? 1000 : INDEX_SOFT_DELETES_RETENTION_LEASE_PERIOD_SETTING.get(Settings.EMPTY).millis()
                    )
                ).getStringRep()
            );
        }