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
private void loadOrExecuteQueryPhase(final ShardSearchRequest request, final SearchContext context) throws Exception {
        final boolean canCache = IndicesService.canCache(request, context);
        context.getSearchExecutionContext().freezeContext();
        if (canCache) {
            indicesService.loadIntoContext(request, context);
        } else {
            QueryPhase.execute(context);
        }
    }
    public void executeQueryPhase(ShardSearchRequest request, SearchShardTask task, ActionListener<SearchPhaseResult> listener) {
        assert request.canReturnNullResponseIfMatchNoDocs() == false || request.numberOfShards() > 1
            : "empty responses require more than one shard";
        final IndexShard shard = getShard(request);
        rewriteAndFetchShardRequest(shard, request, listener.delegateFailure((l, orig) -> {
            
            if (orig.canReturnNullResponseIfMatchNoDocs()) {
                assert orig.scroll() == null;
                final CanMatchShardResponse canMatchResp;
                try {
                    ShardSearchRequest clone = new ShardSearchRequest(orig);
                    canMatchResp = canMatch(clone, false);
                } catch (Exception exc) {
                    l.onFailure(exc);
                    return;
                }
                if (canMatchResp.canMatch() == false) {
                    l.onResponse(QuerySearchResult.nullInstance());
                    return;
                }
            }