to be fair, the main selling point of mongodb is that developers can access it more easily. i haven't really touched mongodb in over a year and then only for playing, but have you tried the elasticsearch filter query syntax? have you compared mongodbs syntax?
also, i have the exact opposite nitpick. people want to use it to do everything, mail indexers, file system indexers. what's the matter with web developer folks? why is it that when the next database comes around they want to use it for everything?