Doesn't that invalidate safety net?
Sorry I'm not 100% sure what your asking. If you're asking about custom roms, I'd trust many custom roms (Graphene is my favorite) better than a lot of manufacturers's roms. And a bootloader that can be re-locked is a big boost to security, since it requires that the OS be signed by the devs instead of making it easier for malicious code to be shimmed in and run at the OS level even if I install a custom operating system.