That's a likely outcome, but it doesn't have to be. The settings UI could allow me to install new keys off USB, and then set a password to prevent someone else from doing the same thing. Security doesn't have to mean giving up control of your own system (Microsoft's requirements for UEFI Secure Boot on x86 systems get this precisely correct)
It's difficult enough to get a correct implementation of secure boot as it is, and while adding your own keys is nice in theory, it also means that the manufacturer would have to do more work to add that functionality. In the case of secure boot it was MS's requirements that persuaded them to (probably reluctantly) do it, but there's nothing of that sort for smart TVs and the like. On the other hand, there's plenty of pressure by media corporations to lock things down for DRM. Thus, even if there was functionality that enabled you to truly "own" your device by making it trust you, it would undoubtedly also come with its own restrictions (e.g. disabling access to DRM'd content, future updates, etc.), so in some ways it segregates and stigmatises.
So while I agree that "secure, full control" > "insecure, full control" > "secure, no control", since the first option is highly unlikely and efforts toward more security are probably going to result in the last one, I think the middle option isn't that bad after all...
