What freedom do you need beyond replacing the OS, which is possible on all phones Google sells? If you want to replace the radio firmware, that isn't something that would be possible without that duopoly either.
So, yes, I can buy a phone that I can mostly control (at the risk of losing access to some draconian apps). But most devices being sold don't allow consumer control.
Doing crazy things like taking a backup of the phone which you paid full price for?