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
return searchContext;
    }
    int determineMaximumNumberOfSlices(ExecutorService executor, ShardSearchRequest request, ResultsType resultsType) {
        return executor instanceof ThreadPoolExecutor tpe
            && isParallelCollectionSupportedForResults(resultsType, request.source(), this.enableQueryPhaseParallelCollection)
                ? tpe.getMaximumPoolSize()
                : 1;
    }
    static boolean isParallelCollectionSupportedForResults(
        ResultsType resultsType,
        SearchSourceBuilder source,
        boolean isQueryPhaseParallelismEnabled
    ) {
        if (resultsType == ResultsType.DFS) {
            return true;
        }
        if (resultsType == ResultsType.QUERY && isQueryPhaseParallelismEnabled) {
            return source == null || source.supportsParallelCollection();
        }
        return false;
    }
    private void freeAllContextForIndex(Index index) {
        assert index != null;
        for (ReaderContext ctx : activeReaders.values()) {
            if (index.equals(ctx.indexShard().shardId().getIndex())) {
                freeReaderContext(ctx.id());
            }
        }
    }
    private void freeAllContextsForShard(ShardId shardId) {