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/ESSingleNodeTestCase.java
if (enableConcurrentSearch) {
            settingBuilder.put(SearchService.QUERY_PHASE_PARALLEL_COLLECTION_ENABLED.getKey(), true)
                .put(SearchService.MINIMUM_DOCS_PER_SLICE.getKey(), 1);
        }
        Settings settings = settingBuilder.build();
        Collection<Class<? extends Plugin>> plugins = new ArrayList<>(getPlugins());
        if (plugins.contains(getTestTransportPlugin()) == false) {
            plugins.add(getTestTransportPlugin());
        }
        if (addMockHttpTransport()) {
            plugins.add(MockHttpTransport.TestPlugin.class);
        }
        if (enableConcurrentSearch) {
            plugins.add(ConcurrentSearchTestPlugin.class);
        }
        plugins.add(MockScriptService.TestPlugin.class);
        Node node = new MockNode(settings, plugins, forbidPrivateIndexSettings());
        try {
            node.start();
        } catch (NodeValidationException e) {
            throw new RuntimeException(e);
        }
        return node;
    }
    /**
     * Returns a client to the single-node cluster.
     */
    public Client client() {
        return wrapClient(NODE.client());
    }