Let's say I want to secure my system against an app developer deciding to delete my data stored in their app.
To do that, I wish to store a copy of all the files the app has written to my filesystem, and put that copy outside the app's control. This is explicitly to contain data the app's developer does not WANT me to be able to keep.
A. Is my being unable to do this "more secure"? If so, why is the specific threat I described to my data integrity - an app developer deleting my data - invalid?
B. Does GrapheneOS support this protection, ensuring the device owner is secure against the app developer, or do they instead secure the app developer against the user?
Let's say you are a Graphene OS user. Why are you even using such an app?
Also you are misrepresenting the threat model. The problem is not an app deleting it's own legitimate data.
P.S. On GrapheneOS you can block apps from getting Internet access to limit their bad ideas.