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 minNumDataNodes;
        int maxNumDataNodes;
        if (numDataNodes >= 0) {
            minNumDataNodes = maxNumDataNodes = numDataNodes;
        } else {
            minNumDataNodes = getMinNumDataNodes();
            maxNumDataNodes = getMaxNumDataNodes();
        }
        Collection<Class<? extends Plugin>> mockPlugins = getMockPlugins();
        final NodeConfigurationSource nodeConfigurationSource = getNodeConfigSource();
        if (addMockTransportService()) {
            ArrayList<Class<? extends Plugin>> mocks = new ArrayList<>(mockPlugins);
            
            
            if (mockPlugins.contains(getTestTransportPlugin()) == false) {
                mocks.add(getTestTransportPlugin());
            }
            mockPlugins = mocks;
        }
        return new InternalTestCluster(
            seed,
            createTempDir(),
            supportsDedicatedMasters,
            getAutoManageMasterNodes(),
            minNumDataNodes,
            maxNumDataNodes,
            InternalTestCluster.clusterName(scope.name(), seed) + "-cluster",
            nodeConfigurationSource,
            getNumClientNodes(),
            nodePrefix,