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
docIdsToLoad = new int[numSuggestDocs];
            } else {
                int totalSize = context.from() + context.size();
                docIdsToLoad = new int[Math.min(topDocs.scoreDocs.length - context.from(), context.size()) + numSuggestDocs];
                for (int i = context.from(); i < Math.min(totalSize, topDocs.scoreDocs.length); i++) {
                    docIdsToLoad[docsOffset++] = topDocs.scoreDocs[i].doc;
                }
            }
        }
        for (CompletionSuggestion completionSuggestion : completionSuggestions) {
            for (CompletionSuggestion.Entry.Option option : completionSuggestion.getOptions()) {
                docIdsToLoad[docsOffset++] = option.getDoc().doc;
            }
        }
        context.docIdsToLoad(docIdsToLoad);
    }
    private static void processScroll(InternalScrollSearchRequest request, ReaderContext reader, SearchContext context) {
        
        context.from(context.from() + context.size());
        context.scrollContext().scroll = request.scroll();
    }
    /**
     * Returns the number of active contexts in this
     * SearchService
     */
    public int getActiveContexts() {
        return this.activeReaders.size();
    }
    /**
     * Returns the number of scroll contexts opened on the node