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
}
            context.sliceBuilder(source.slice());
        }
        if (source.storedFields() != null) {
            if (source.storedFields().fetchFields() == false) {
                if (context.sourceRequested()) {
                    throw new SearchException(shardTarget, "[stored_fields] cannot be disabled if [_source] is requested");
                }
                if (context.fetchFieldsContext() != null) {
                    throw new SearchException(shardTarget, "[stored_fields] cannot be disabled when using the [fields] option");
                }
            }
            context.storedFieldsContext(source.storedFields());
        }
        if (source.collapse() != null) {
            if (context.scrollContext() != null) {
                throw new SearchException(shardTarget, "cannot use `collapse` in a scroll context");
            }
            if (context.rescore() != null && context.rescore().isEmpty() == false) {
                throw new SearchException(shardTarget, "cannot use `collapse` in conjunction with `rescore`");
            }
            final CollapseContext collapseContext = source.collapse().build(searchExecutionContext);
            context.collapse(collapseContext);
        }
        if (source.rankBuilder() != null) {
            List<Query> queries = new ArrayList<>();
            for (SubSearchSourceBuilder subSearchSourceBuilder : source.subSearches()) {
                queries.add(subSearchSourceBuilder.toSearchQuery(context.getSearchExecutionContext()));
            }
            context.rankShardContext(source.rankBuilder().buildRankShardContext(queries, context.from()));