He does have a point - but only if you want to do something more complex. If you need a JSON store that you can easily edit, I don't see a real advantage over Firebase - but once you want to incorporate, say Twitter login or some form of user authentication for your visitors, you're better off with Firebase, I would say.
Because Firebase has a well written and documented API The best advantage of Firebase is it's realtime and it's blazing fast. You can create collaborative apps without worrying the backend.
I don't want to change the topic, however it's a great tip. Firebase should be used for more complex things.