One benefit to ES is scale. Elasticsearch can scale to at least a couple trillion records (on the order of 1.5 PB) if you spread your data out across enough hardware. You can then search those records in seconds (for simple queries). I'm not sure Mongo can scale quite that far, it was given up on before I started this work. Not saying it can't, just saying others had more success scaling ES and haven't really hit its limits. Bear in mind datasets span multiple clusters and are searches are merged using cross cluster search in these larger cases. Not likely to be an apples to apples comparison.