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
final boolean hasRefreshPending;
            final Engine.Searcher canMatchSearcher;
            if (request.readerId() != null) {
                hasRefreshPending = false;
                ReaderContext readerContext;
                Engine.Searcher searcher;
                try {
                    readerContext = findReaderContext(request.readerId(), request);
                    releasable = readerContext.markAsUsed(getKeepAlive(request));
                    indexService = readerContext.indexService();
                    if (canMatchAfterRewrite(request, indexService) == false) {
                        return new CanMatchShardResponse(false, null);
                    }
                    searcher = readerContext.acquireSearcher(Engine.CAN_MATCH_SEARCH_SOURCE);
                } catch (SearchContextMissingException e) {
                    final String searcherId = request.readerId().getSearcherId();
                    if (searcherId == null) {
                        throw e;
                    }
                    indexService = indicesService.indexServiceSafe(request.shardId().getIndex());
                    if (canMatchAfterRewrite(request, indexService) == false) {
                        return new CanMatchShardResponse(false, null);
                    }
                    IndexShard indexShard = indexService.getShard(request.shardId().getId());
                    final Engine.SearcherSupplier searcherSupplier = indexShard.acquireSearcherSupplier();
                    if (searcherId.equals(searcherSupplier.getSearcherId()) == false) {
                        searcherSupplier.close();
                        throw e;
                    }
                    releasable = searcherSupplier;