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
server/src/main/java/org/elasticsearch/search/SearchService.java
);
    public static final Setting<ByteSizeValue> MAX_ASYNC_SEARCH_RESPONSE_SIZE_SETTING = Setting.byteSizeSetting(
        "search.max_async_search_response_size",
        new ByteSizeValue(10, ByteSizeUnit.MB),
        Property.Dynamic,
        Property.NodeScope
    );
    public static final int DEFAULT_SIZE = 10;
    public static final int DEFAULT_FROM = 0;
    private final ThreadPool threadPool;
    private final ClusterService clusterService;
    private final IndicesService indicesService;
    private final ScriptService scriptService;
    private final ResponseCollectorService responseCollectorService;
    private final ExecutorSelector executorSelector;
    private final BigArrays bigArrays;
    private final DfsPhase dfsPhase = new DfsPhase();
    private final FetchPhase fetchPhase;
    private volatile boolean enableSearchWorkerThreads;
    private volatile boolean enableQueryPhaseParallelCollection;
    private volatile long defaultKeepAlive;
    private volatile long maxKeepAlive;
    private volatile TimeValue defaultSearchTimeout;
    private final int minimumDocsPerSlice;
    private volatile boolean defaultAllowPartialSearchResults;
    private volatile boolean lowLevelCancellation;
    private volatile int maxOpenScrollContext;
    private volatile boolean enableRewriteAggsToFilterByFilter;
    private final Cancellable keepAliveReaper;
    private final AtomicLong idGenerator = new AtomicLong();