All you do is poop all over the story about postgres. I'm convinced that no use cases will convince you of anything. I'm not really looking to involve myself in a database holy war.
Your response seems to betray a certain ignorance of mongo. Don't you realize that mongo has indexes?
For handling documents, this blog post covers the topic in some depth.
https://jimb-cc.medium.com/postgres-jsonb-meets-mongodb-part...
Might I suggest you actually use mongo on a project before engaging further on the topic. It clearly has had a lot more thought put into it in the context of json documents.
If postgres works great for your use cases, great, go be happy with the tool.
But a query language within a query language feels bolted onto something alien to do something pretty basic. Pass. If I'm teaching this to new engineers, pass also.