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
if (random.nextBoolean()) {
            builder.put(IndicesRequestCache.INDEX_CACHE_REQUEST_ENABLED_SETTING.getKey(), random.nextBoolean());
        }
        if (random.nextBoolean()) {
            builder.put(IndexSettings.INDEX_CHECK_ON_STARTUP.getKey(), randomFrom(random, "false", "checksum", "true"));
        }
        if (random.nextBoolean()) {
            
            builder.put(
                UnassignedInfo.INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING.getKey(),
                RandomNumbers.randomIntBetween(random, 1, 15) + "ms"
            );
        }
        if (randomBoolean()) {
            builder.put(IndexSettings.BLOOM_FILTER_ID_FIELD_ENABLED_SETTING.getKey(), randomBoolean());
        }
        return builder;
    }
    private static Settings.Builder setRandomIndexMergeSettings(Random random, Settings.Builder builder) {
        if (random.nextBoolean()) {
            builder.put(
                MergePolicyConfig.INDEX_COMPOUND_FORMAT_SETTING.getKey(),
                (random.nextBoolean() ? random.nextDouble() : random.nextBoolean()).toString()
            );
        }
        switch (random.nextInt(4)) {
            case 3 -> {
                final int maxThreadCount = RandomNumbers.randomIntBetween(random, 1, 4);
                final int maxMergeCount = RandomNumbers.randomIntBetween(random, maxThreadCount, maxThreadCount + 4);
                builder.put(MergeSchedulerConfig.MAX_MERGE_COUNT_SETTING.getKey(), maxMergeCount);