Right. Just like MySQL/Oracle was put out to pasture.
And if you think MongoDB is only popular because it is a JSON store then it shows just little you know about the database landscape and about how developers actually use databases.
For those of us that use all 3 of those, your statement is in large part true. I'd also hazard that Mongodb isn't actually that popular outside the HN buzz bubble.
"Mongodb" already nearly exists as a single column type, 9.4 will complete it.