> An example of this might be the Facebook app. Currently it's only available in the official App Store where by design Apple, on our behalf, defines and enforces policies that protect the users.

My counterargument to that is even the current status quo doesn't work for privacy. Facebook can still get less data from the browser version compared to the app and that's why they are pushing hard for an app install. What would work is tighter sandboxing similar to the web, not custom reviews.