I like and respect your choice of using firebase but I don't know why the whole community is making tons of tutorials on firebase. Like firebase is good for testing but never for production so try using actual databses.
This video/article is mostly for beginners and helps them build a real-time application in no time.
The Firebase is pretty powerful for making this kind of applications and for prototyping things very quickly.
But I agree that's not the only solution out there and probably not the best one for all applications. I often use MongoDB as the database for most of my applications.
If you are interested in any other kind of technology, please let me know. I'd be happy to make a video or write an article about it.