You use operating systems that have significantly worse security than GOS, iOS and even stock Android as your examples?
Also you literally are the owner with GrapheneOS, lacking security is not "full ownership." You can create your own build of GOS, you can modify it ahead of time, you can literally see all of the source code it's running.
Claiming GOS isn't true ownership is like complaining that you can't change your car's wheel alignment while driving it and saying it means you don't truly own your car.