Alternative OSes surely do have better privacy than Android, but that’s probably not sufficient. On Smartphones, there runs not a single CPU like on a laptop, but more like 5 computers and only one of them is controlled by the OS. For example, there is a baseband processor and a radio modem. And the SIM card is a computer. And part of these can be controlled remotely (have you ever wondered how your phone automatically re-programs it parameters when you change providers?).

And then there are gaps in authentication in the radio prozocol: Your phone / SIM card authenticates against a radio tower so that the right phone user pays the bill. But the phone has no way to detect a rogue mobile tower…

It seems to be just accepted that everyone is going to jump to another company every couple years (usually due to companies not giving adequate raises).

Well. I did the last jump because the quality was so bad.