Same, exactly what I do. For the part about backups, there are tools that make it really easy. I’m using databasus for instance. Once I had set up a couple applications, adding a new db, user, and backup config took just a few minutes every time really. In the end figuring out how to backup every docker stack’s individual DB sounds more complicated to me.

Edit: plus my first service hosted in this lab was my own matrix instance so I needed a solid DB, then it was already there so might as well use it.