Its similar to what the Linux distributions that try to turn on a SeLinux like profile by default would feel like if they really put in the work. That's nothing like switching (from a Linux) to a BSD.
(I would love to just run my desktop Linux with a half baked touch UI and rely on browser versions of almost everything, but that would feel like a real switch between OSes instead of just seeing the same OS with a corrected security profile as the user. I also don't see why you compare it to an Abrams, I doubt an Abrams has a security model intentionally compromised by an ad company, GrapheneOS just makes it possible to catch the dumbest or laziest attacks on a system no one should run ever.)