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 (context.queryResult().hasSearchContext() == false && readerContext.singleSession()) {
                    freeReaderContext(readerContext.id());
                }
                afterQueryTime = executor.success();
            } finally {
                tracer.stopTrace(spanId);
            }
            if (request.numberOfShards() == 1 && (request.source() == null || request.source().rankBuilder() == null)) {
                
                context.addFetchResult();
                return executeFetchPhase(readerContext, context, afterQueryTime);
            } else {
                
                
                final RescoreDocIds rescoreDocIds = context.rescoreDocIds();
                context.queryResult().setRescoreDocIds(rescoreDocIds);
                readerContext.setRescoreDocIds(rescoreDocIds);
                context.queryResult().incRef();
                return context.queryResult();
            }
        } catch (Exception e) {
            
            if (e instanceof ExecutionException) {
                e = (e.getCause() == null || e.getCause() instanceof Exception)
                    ? (Exception) e.getCause()
                    : new ElasticsearchException(e.getCause());
            }
            logger.trace("Query phase failed", e);
            processFailure(readerContext, e);
            throw e;