From your link, go to https://newbiedba.wordpress.com/2017/11/27/thoughts-on-postg... for the followup after he wrote those benchmarks. When he ran his benchmarks, he indeed got better throughput on MongoDB. But the 99% performance was massively worse - in fact slow enough to be unacceptable. To an extent that he concluded that you'd be better off using PostgreSQL.

And he's right. As pages like http://latencytipoftheday.blogspot.com/2014/06/latencytipoft... make clear, we have a lot of calls back to the application happening. Users will notice the occasional slow load surprisingly quickly, and it is worth a lot to get rid of them.

So even your chosen source agrees. A relational database is not orders of magnitude slower. In fact, a relational database is probably a better fit.