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
return annotation == null || annotation.maxNumDataNodes() == -1
            ? InternalTestCluster.DEFAULT_MAX_NUM_DATA_NODES
            : annotation.maxNumDataNodes();
    }
    private int getNumClientNodes() {
        ClusterScope annotation = getAnnotation(this.getClass(), ClusterScope.class);
        return annotation == null ? InternalTestCluster.DEFAULT_NUM_CLIENT_NODES : annotation.numClientNodes();
    }
    /**
     * This method is used to obtain settings for the {@code N}th node in the cluster.
     * Nodes in this cluster are associated with an ordinal number such that nodes can
     * be started with specific configurations. This method might be called multiple
     * times with the same ordinal and is expected to return the same value for each invocation.
     * In other words subclasses must ensure this method is idempotent.
     */
    protected Settings nodeSettings(int nodeOrdinal, Settings otherSettings) {
        Settings.Builder builder = Settings.builder()
            .put(DestructiveOperations.REQUIRES_NAME_SETTING.getKey(), false)
            
            
            .put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK_SETTING.getKey(), "1b")
            .put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK_SETTING.getKey(), "1b")
            .put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_DISK_FLOOD_STAGE_WATERMARK_SETTING.getKey(), "1b")
            
            
            
            .put(IndicesQueryCache.INDICES_QUERIES_CACHE_ALL_SEGMENTS_SETTING.getKey(), nodeOrdinal % 2 == 0)
            
            .put(IndicesStore.INDICES_STORE_DELETE_SHARD_TIMEOUT.getKey(), new TimeValue(1, TimeUnit.SECONDS))