I believe you got it backwards. When the device is open, it can protect one's privacy. The problem is, we don't have open devices. I mean, tha hardware is not

I believe you got it backwards. When the device is open, it can protect one's privacy. The problem is, we don't have open devices. I mean, tha hardware is not open, so developers can't generally implement any proper secure boot schemes (starting from a trusted bootloader), and can't generally control what goes on in the radio modules. Because there are no devices that have those parts open (or I'm unaware of something I want to buy?), there's no security/privacy possible. Apple can provide privacy there because they're damn huge and they can purchase or design any hardware they want, fully documented to the last every single logic gate. An average free software developer can't. As for the userland - I believe there are AOSP derivatives + 3rd party apps that result in a reasonably good privacy and security experience.