Lucene (what Elasticsearch and Solr use) are based on inverted indexes which is what the GIN in the article also uses. So the benefits of ES/etc are being able

Lucene (what Elasticsearch and Solr use) are based on inverted indexes which is what the GIN in the article also uses. So the benefits of ES/etc are being able to scale horizontally scale across nodes or any additional features it adds on top of the main index.