I learned German at a University in a German speaking country, and the classes were completely in German from day one which I found helpful. I also bought quite a number of books and studied quite a lot before I become fluent.
So I don’t think an app is a one stop solution, it takes a lot of material, I’m not sure why people think any one system is enough, especially considering you never stop learning a language. Fluent just means you know enough to continue to learn in the language on your own.