The author is talking about a different classes of rdbms. I believe his intention was not to compare PostgreSQL to ElasticSearch or ClickHouse which will solve

The author is talking about a different classes of rdbms. I believe his intention was not to compare PostgreSQL to ElasticSearch or ClickHouse which will solve a completely different problem. But for small to medium datasets his advice to just stick to PostgreSQL is good: Start with an easy solution which will give you anything you need (by simply installing a plugin). If you need more specialized software THEN use it, but don't start with an overcomplicated stack because ElasticSearch and ClickHouse may be the state-of-the-art open source solution to a specific problem.