This is the thing I find when people post "ElasticSearch Alternative".

80% of ElasticSearch's value add (wrt search anyway) is all the clustering and frame work that allows you to span the search over tens or hundreds of machines "easily".

I think the same is true here. Probably the comparison should be with the underlying search libraries that ES sits on.

I suppose this comparison makes sense in a world where most people don't run their own servers much any more since the clustering etc would be a problem for the cloud offering and not the consumer.