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
}
    private static void ensureClusterInfoServiceRunning() {
        if (isInternalCluster() && cluster().size() > 0) {
            
            refreshClusterInfo();
        }
    }
    public static void refreshClusterInfo() {
        final ClusterInfoService clusterInfoService = internalCluster().getInstance(
            ClusterInfoService.class,
            internalCluster().getMasterName()
        );
        if (clusterInfoService instanceof InternalClusterInfoService) {
            ClusterInfoServiceUtils.refresh(((InternalClusterInfoService) clusterInfoService));
        }
    }
    /**
     * Ensures the cluster is in a searchable state for the given indices. This means a searchable copy of each
     * shard is available on the cluster.
     */
    protected ClusterHealthStatus ensureSearchable(String... indices) {
        
        return ensureGreen(indices);
    }
    protected void ensureStableCluster(int nodeCount) {
        ensureStableCluster(nodeCount, TimeValue.timeValueSeconds(30));
    }
    protected void ensureStableCluster(int nodeCount, TimeValue timeValue) {
        ensureStableCluster(nodeCount, timeValue, false, null);
    }