I've found OpenSearch to be a bit flaky but I haven't worked with it very seriously compared to ElasticSearch
(and before OpenSearch, the AWS-managed ElasticSearch absolutely hurt the ElasticSearch brand because of all of the issues Amazon created - it couldn't even rebalance shards, let alone add new nodes or switch to larger nodes without a blue-green deployment)
Elastic bought found.no, which became Elastic Cloud in 2015. That was years before Amazon forked Opensearch. The AWS hosted Elasticsearch emerged around the same time.
(and before OpenSearch, the AWS-managed ElasticSearch absolutely hurt the ElasticSearch brand because of all of the issues Amazon created - it couldn't even rebalance shards, let alone add new nodes or switch to larger nodes without a blue-green deployment)