"This makes the point that the real battle we should be fighting is not for control of Android/iOS, but the ability to run other operating systems on phones."
Sometimes owner control, cf. corporate control, can be had by sacrificing hardware functionality, i.e., features, closed source drivers. Choice between particular hardware feature(s) working and control over the hardware in general.
Yes but in the phone space the sacrifice is too much. You often times forgo the ability to even participate in many aspects of society, e.g. banking. It's not your typical "rough around the edges open source alternative", it's just not even a comparison.
Have at least two phones. One with corporate OS for banking, commerce. Another with user-chosen OS for experimentation, able to boot from external media.