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
assert routing.initializing();
        if (routing.isRelocationTarget() == false) {
            freeAllContextsForShard(routing.shardId());
        }
    }
    protected void putReaderContext(ReaderContext context) {
        final ReaderContext previous = activeReaders.put(context.id().getId(), context);
        assert previous == null;
        
        
        final Index index = context.indexShard().shardId().getIndex();
        if (indicesService.hasIndex(index) == false) {
            removeReaderContext(context.id().getId());
            throw new IndexNotFoundException(index);
        }
    }
    protected ReaderContext removeReaderContext(long id) {
        return activeReaders.remove(id);
    }
    @Override
    protected void doStart() {}
    @Override
    protected void doStop() {
        for (final ReaderContext context : activeReaders.values()) {
            freeReaderContext(context.id());
        }
    }