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
if (contextId != null) {
            if (sessionId.equals(contextId.getSessionId())) {
                final ReaderContext readerContext = activeReaders.get(contextId.getId());
                if (readerContext != null) {
                    return readerContext.indexShard();
                }
            }
        }
        return indicesService.indexServiceSafe(request.shardId().getIndex()).getShard(request.shardId().id());
    }
    private static <T> void runAsync(Executor executor, CheckedSupplier<T, Exception> executable, ActionListener<T> listener) {
        executor.execute(ActionRunnable.supply(listener, executable));
    }
    /**
     * The returned {@link SearchPhaseResult} will have had its ref count incremented by this method.
     * It is the responsibility of the caller to ensure that the ref count is correctly decremented
     * when the object is no longer needed.
     */
    private SearchPhaseResult executeQueryPhase(ShardSearchRequest request, SearchShardTask task) throws Exception {
        final ReaderContext readerContext = createOrGetReaderContext(request);
        SpanId spanId = SpanId.forTask(task);
        try (
            Releasable scope = tracer.withScope(spanId);
            Releasable ignored = readerContext.markAsUsed(getKeepAlive(request));
            SearchContext context = createContext(readerContext, request, task, ResultsType.QUERY, true)
        ) {
            tracer.startTrace("executeQueryPhase", Map.of());
            final long afterQueryTime;
            try (SearchOperationListenerExecutor executor = new SearchOperationListenerExecutor(context)) {
                loadOrExecuteQueryPhase(request, context);