GrapheneOS is more well-roundedly private than any desktop OS.
Competition is Qubes but that has usability issues and does not have good hardware security.
I'm not about to trust a google branded device. Even if the Graphene folks are on the up and up, google sure as hell isn't.
The problem for me is writing on a mobile device is a terrible user experience.
When I'm at home I don't wanna use a virtual keyboard on a 6.3" (or 7.9 unfolded). I just want to use my triple monitor PC setup with a real keyboard and a wealth of display space.
Mobile is cool for on the go but a productivity killer.