Ah, I see. Thank you - I think I can envision the experience that you have in mind. I also think that your concern - users being confused - is quite valid and very customer focused.
What I'm gathering is that you are describing a specific implementation of the feature, "have individual volume controls for each app", based on how you think it might work. Also, in your opinion, that implementation would be confusing for users (I see your point here as well). Alas, that is only one of the ways in which this feature could be implemented. There may be many others, that we aren't considering at this time, that you or the majority of other users would not find confusing.
We should be careful to not conflate the feature and an implementation of the feature. An implementation of an idea being problematic does not automatically mean that the idea itself was problematic. It may simply mean we have more work to do in order to find an implementation that meets all the constraints under consideration.
That is where you would expect to change the volume of an app.
I like this note as well. Still, there was also a time when users expected phones to have a physical keypad. A certain company blew that idea out of the water and changed the world in the process. Sometimes the right thing to do is exactly what the user expects. And still sometimes, you have to innovate and break the status quo. In all cases, I think each path should be carefully explored with adequate user research (as much as time and finances will allow) before a judgement is made as to what is feasible.
