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
import org.elasticsearch.search.fetch.ScrollQueryFetchSearchResult;
import org.elasticsearch.search.fetch.ShardFetchRequest;
import org.elasticsearch.search.fetch.subphase.FetchDocValuesContext;
import org.elasticsearch.search.fetch.subphase.FetchFieldsContext;
import org.elasticsearch.search.fetch.subphase.ScriptFieldsContext.ScriptField;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
import org.elasticsearch.search.internal.AliasFilter;
import org.elasticsearch.search.internal.InternalScrollSearchRequest;
import org.elasticsearch.search.internal.LegacyReaderContext;
import org.elasticsearch.search.internal.ReaderContext;
import org.elasticsearch.search.internal.SearchContext;
import org.elasticsearch.search.internal.ShardSearchContextId;
import org.elasticsearch.search.internal.ShardSearchRequest;
import org.elasticsearch.search.internal.SubSearchContext;
import org.elasticsearch.search.lookup.SearchLookup;
import org.elasticsearch.search.profile.Profilers;
import org.elasticsearch.search.query.QueryPhase;
import org.elasticsearch.search.query.QuerySearchRequest;
import org.elasticsearch.search.query.QuerySearchResult;
import org.elasticsearch.search.query.ScrollQuerySearchResult;
import org.elasticsearch.search.rescore.RescorerBuilder;
import org.elasticsearch.search.searchafter.SearchAfterBuilder;
import org.elasticsearch.search.sort.FieldSortBuilder;
import org.elasticsearch.search.sort.MinAndMax;
import org.elasticsearch.search.sort.SortAndFormats;
import org.elasticsearch.search.sort.SortBuilder;
import org.elasticsearch.search.suggest.Suggest;
import org.elasticsearch.search.suggest.completion.CompletionSuggestion;
import org.elasticsearch.tasks.TaskCancelledException;
import org.elasticsearch.telemetry.tracing.SpanId;