While everything you said is true, there's one big problem: even if you isolate the baseband and treat it as hostile, there are some things that it is able to d

While everything you said is true, there's one big problem: even if you isolate the baseband and treat it as hostile, there are some things that it is able to do on its own and no amount of sandboxing can fix it. By design, a baseband is able to track and report your location in real time without ever involving anything outside its silicon. Most basebands are also hooked directly into the microphone and maybe even camera. Since all but a handful of phones have the necessary hardware allowing the CPU to disconnect the baseband from the mic/camera, no amount of clever software can stop a compromised baseband from eavesdropping and even with special hardware, unless you're willing to cut power completely, it will always be able to track you.