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
ensureAfterSeqNoRefreshed(shard, orig, () -> executeQueryPhase(orig, task), l);
        }));
    }
    private <T> void ensureAfterSeqNoRefreshed(
        IndexShard shard,
        ShardSearchRequest request,
        CheckedSupplier<T, Exception> executable,
        ActionListener<T> listener
    ) {
        final long waitForCheckpoint = request.waitForCheckpoint();
        final Executor executor = getExecutor(shard);
        try {
            if (waitForCheckpoint <= UNASSIGNED_SEQ_NO) {
                runAsync(executor, executable, listener);
                return;
            }
            if (shard.indexSettings().getRefreshInterval().getMillis() <= 0) {
                listener.onFailure(new IllegalArgumentException("Cannot use wait_for_checkpoints with [index.refresh_interval=-1]"));
                return;
            }
            final AtomicBoolean isDone = new AtomicBoolean(false);
            
            
            final TimeValue timeout = request.getWaitForCheckpointsTimeout();
            final Scheduler.ScheduledCancellable timeoutTask = NO_TIMEOUT.equals(timeout) ? null : threadPool.schedule(() -> {
                if (isDone.compareAndSet(false, true)) {
                    listener.onFailure(
                        new ElasticsearchTimeoutException("Wait for seq_no [{}] refreshed timed out [{}]", waitForCheckpoint, timeout)
                    );
                }