This comes from experience with SQL Server, not postgres and lucene instead of elastic search, but no, I don't think full-text search replaces lucene/elastic for any but the simplest searches. Especially if you want to rank results based on a number of factors, not just a text match. The last time I was using them for instance, we wanted geographic location to be weighted strongly and the database approach did not under performed on result speed, result accuracy and developer time (excluding learning lucene, which isn't that hard anyway).