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 shardId != null;
        for (ReaderContext ctx : activeReaders.values()) {
            if (shardId.equals(ctx.indexShard().shardId())) {
                freeReaderContext(ctx.id());
            }
        }
    }
    public boolean freeReaderContext(ShardSearchContextId contextId) {
        if (sessionId.equals(contextId.getSessionId())) {
            try (ReaderContext context = removeReaderContext(contextId.getId())) {
                return context != null;
            }
        }
        return false;
    }
    public void freeAllScrollContexts() {
        for (ReaderContext readerContext : activeReaders.values()) {
            if (readerContext.scrollContext() != null) {
                freeReaderContext(readerContext.id());
            }
        }
    }
    private long getKeepAlive(ShardSearchRequest request) {
        if (request.scroll() != null) {
            return getScrollKeepAlive(request.scroll());
        } else if (request.keepAlive() != null) {
            checkKeepAliveLimit(request.keepAlive().millis());
            return request.keepAlive().getMillis();
        } else {
            return request.readerId() == null ? defaultKeepAlive : -1;