I've read a lot more about "how dumb it is to use mongo over PG" than the opposite, I think the burden of proof is on the mongo-lovers these days (not that anyone has to prove anything to randos on the internet)

Why mongo is dumb has been written up about ad nauseam - from data modeling and quality issues, out of control costs, etc. It's been a known toxic dumpsterfire for well over a decade...