I agree with most of your post. I completed the Busuu French course, it was okay and much better than Duolingo, but like all of these apps, it’s only a starter course. I tried the Busuu German course, but gave up as there was too much grammar being introduced, and I got lost. I did the Babbel German course, which I preferred. Again, it’s only a starter course. All these online apps are little more than glorified SRS.
I think apps are good for novices, they provide a framework, but I can’t help thinking a proper course with group lessons would be better. Anyone with at least one L2 learnt as an adult to a high level should be able to learn independently without an app.
There is a trend to dismiss school teaching, and promote apps as the modern way to learn. I can’t help thinking that such ideas were promoted by the app creators.