I agree with you, but even with the ability to install your own OS properly, you can't necessarily use some of the hardware.

As I recall from Ubuntu Touch, they had to build a system that was a thin wrapper around Android so that they had access to firmware blobs.

I guess that would still be ok as long as the hardware component manufacturers don't start to require authentication from the OS. That would be along the same lines as the fight you're describing.

I think that for the first step, we need to make sure that AOSP forks can work. And those can just copy the binary blobs.

Don't get me wrong: I like all alternatives. But the most realistic alternative to Stock Android is based on AOSP. In good approximation, today nobody would want anything else.

If we get there, then the next step is to get open source firmwares. But I don't know much about that and it feels like it is a much harder fight. Hardware manufacturers probably strongly believe that they will lose their competitive advantage if they open source their firmwares, and I don't know how true that is.