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
throw new IllegalArgumentException("Session id must be specified");
        }
        if (sessionId.equals(id.getSessionId()) == false) {
            throw new SearchContextMissingException(id);
        }
        final ReaderContext reader = activeReaders.get(id.getId());
        if (reader == null) {
            throw new SearchContextMissingException(id);
        }
        try {
            reader.validate(request);
        } catch (Exception exc) {
            processFailure(reader, exc);
            throw exc;
        }
        return reader;
    }
    final ReaderContext createOrGetReaderContext(ShardSearchRequest request) {
        if (request.readerId() != null) {
            try {
                return findReaderContext(request.readerId(), request);
            } catch (SearchContextMissingException e) {
                final String searcherId = request.readerId().getSearcherId();
                if (searcherId == null) {
                    throw e;
                }
                final IndexService indexService = indicesService.indexServiceSafe(request.shardId().getIndex());
                final IndexShard shard = indexService.getShard(request.shardId().id());
                final Engine.SearcherSupplier searcherSupplier = shard.acquireSearcherSupplier();
                if (searcherId.equals(searcherSupplier.getSearcherId()) == false) {