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
try (
                SearchContext searchContext = createContext(readerContext, shardSearchRequest, task, ResultsType.FETCH, false);
                SearchOperationListenerExecutor executor = new SearchOperationListenerExecutor(searchContext)
            ) {
                searchContext.assignRescoreDocIds(readerContext.getRescoreDocIds(null));
                searchContext.searcher().setAggregatedDfs(readerContext.getAggregatedDfs(null));
                processScroll(request, readerContext, searchContext);
                searchContext.addQueryResult();
                QueryPhase.execute(searchContext);
                final long afterQueryTime = executor.success();
                QueryFetchSearchResult fetchSearchResult = executeFetchPhase(readerContext, searchContext, afterQueryTime);
                return new ScrollQueryFetchSearchResult(fetchSearchResult, searchContext.shardTarget());
            } catch (Exception e) {
                assert TransportActions.isShardNotAvailableException(e) == false : new AssertionError(e);
                logger.trace("Fetch phase failed", e);
                
                throw e;
            }
        }, wrapFailureListener(listener, readerContext, markAsUsed));
    }
    public void executeFetchPhase(ShardFetchRequest request, SearchShardTask task, ActionListener<FetchSearchResult> listener) {
        final ReaderContext readerContext = findReaderContext(request.contextId(), request);
        final ShardSearchRequest shardSearchRequest = readerContext.getShardSearchRequest(request.getShardSearchRequest());
        final Releasable markAsUsed = readerContext.markAsUsed(getKeepAlive(shardSearchRequest));
        runAsync(getExecutor(readerContext.indexShard()), () -> {
            try (SearchContext searchContext = createContext(readerContext, shardSearchRequest, task, ResultsType.FETCH, false)) {
                if (request.lastEmittedDoc() != null) {
                    searchContext.scrollContext().lastEmittedDoc = request.lastEmittedDoc();
                }
                searchContext.assignRescoreDocIds(readerContext.getRescoreDocIds(request.getRescoreDocIds()));