I think they are not comparable, for some basic queries maybe PG is enough, but I don't think than the text processing capabilities of lucene are there, and it's ok because one is a database, and the other a search engine. Elastic has drifted a lot to being like a database, but I least for me, what has worked very well is having a database as a source of truth, and denormalizate the database as needed to Solr which is queried by the site. Just something like faceted search navigation, is way easier to do well in Solr or elastic versus PG
