To be fair, both MongoDB and Elasticsearch have had serious issues as pointed out via the Jepsen tests.
https://aphyr.com/posts/317-jepsen-elasticsearch
https://aphyr.com/posts/323-jepsen-elasticsearch-1-5-0
Though, all those issues have been fixed for both MongoDB and Elasticsearch so it's not necessarily fair to judge them based off past performance.
https://www.elastic.co/guide/en/elasticsearch/resiliency/cur...