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
@Override
    protected void doClose() {
        doStop();
        keepAliveReaper.cancel();
    }
    public void executeDfsPhase(ShardSearchRequest request, SearchShardTask task, ActionListener<SearchPhaseResult> listener) {
        final IndexShard shard = getShard(request);
        rewriteAndFetchShardRequest(shard, request, listener.delegateFailure((l, rewritten) -> {
            
            ensureAfterSeqNoRefreshed(shard, request, () -> executeDfsPhase(request, task), l);
        }));
    }
    private DfsSearchResult executeDfsPhase(ShardSearchRequest request, SearchShardTask task) throws IOException {
        ReaderContext readerContext = createOrGetReaderContext(request);
        try (@SuppressWarnings("unused") 
        Releasable scope = tracer.withScope(SpanId.forTask(task));
            Releasable ignored = readerContext.markAsUsed(getKeepAlive(request));
            SearchContext context = createContext(readerContext, request, task, ResultsType.DFS, false)
        ) {
            dfsPhase.execute(context);
            return context.dfsResult();
        } catch (Exception e) {
            logger.trace("Dfs phase failed", e);
            processFailure(readerContext, e);
            throw e;
        }
    }
    /**
     * Try to load the query results from the cache or execute the query phase directly if the cache cannot be used.
     */