Anyway, you’ve just proven my point with “install extensions out of band” - you’ve ceded that it’s a losing position technically and are arguing for alternative UX solutions. I’m not pretending it has to be perfect. Like I said, capabilities are great for creating a secure OS and writing more secure software more generally. But the threat model it’s protecting against is not software that phones home but against the size of the exploit opened up from a compromise.
Think about it this way, Android apps and iOS apps are largely sandboxed through a primitive capabilities system already, not super fine-grained capabilities but still the same concept. Would you care to claim that privacy and malware isn’t a problem on these systems or that the permissions model has meaningfully curtailed anything but the most egregious of problems?