I do not condone or endorse illegal activity. That does not mean your use of GrapheneOS might not be used against you if you use it at an inopportune time. There is currently almost no discussion online about this, so it’s worth a mention.
Edit: I forgot to mention some obvious context in my head. Think journalist, in Russia, using GrapheneOS for “safety.” In such a situation, probably a terrible idea.
A mention, not a core argument against use.
In my reading, your core point is an old argument: https://en.wikipedia.org/wiki/Nothing_to_hide_argument
"You're painting your fence beige instead of white? Are you sure that's a good idea? What if there's a crime committed in the neighborhood - beige-fenced deviants are the first that the police will look at!"
GrapheneOS is likely not a secure system, but neither is any smartphone OS. I'll compliment anyone taking steps towards transparency that makes governments and global-scale corporations tremble at the knees.
Please.