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
test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java
for (IndexRoutingTable indexRoutingTable : clusterState.routingTable()) {
            for (int shardId = 0; shardId < indexRoutingTable.size(); shardId++) {
                final IndexShardRoutingTable indexShard = indexRoutingTable.shard(shardId);
                for (int copy = 0; copy < indexShard.size(); copy++) {
                    ShardRouting shardRouting = indexShard.shard(copy);
                    if (shardRouting.currentNodeId() != null && index.equals(shardRouting.getIndexName())) {
                        String name = clusterState.nodes().get(shardRouting.currentNodeId()).getName();
                        nodes.add(name);
                        assertThat("Allocated on new node: " + name, Regex.simpleMatch(pattern, name), is(true));
                    }
                }
            }
        }
        return nodes;
    }
    /**
     * Asserts that all segments are sorted with the provided {@link Sort}.
     */
    public void assertSortedSegments(String indexName, Sort expectedIndexSort) {
        IndicesSegmentResponse segmentResponse = indicesAdmin().prepareSegments(indexName).execute().actionGet();
        IndexSegments indexSegments = segmentResponse.getIndices().get(indexName);
        for (IndexShardSegments indexShardSegments : indexSegments.getShards().values()) {
            for (ShardSegments shardSegments : indexShardSegments.shards()) {
                for (Segment segment : shardSegments) {
                    assertThat(expectedIndexSort, equalTo(segment.getSegmentSort()));
                }
            }
        }
    }
    protected static class NumShards {