Not sure if I'd use GrapheneOS even if it was available on other devices though. Really not a fan of the hostile attitude towards rooting when it's needed for basic functionality like backups — actual, reliable backups for every app, unlike those provided by the built-in solution.
What I noticed though is that Google often tries to upsell based on software features alone. For example, there is really no point in buying a Pixel 9 Pro instead of a base Pixel 9 as the hardware is practically the same except certain things. But Google markets the Pro model with more software based AI features. When installing GOS this really doesn't make a difference so one can always opt for the more inexpensive models.
The base devices are better value but the Pro devices do mainly differentiate based on hardware. Better display, addition of the 5x telephoto camera, better front camera and more memory are the main selling points. Pixel 9a is similarly a downgrade for the screen, cameras, memory, wireless charging speed and cellular radio (back to a variant of the 7th/8th gen Pixel radio). Pixel 9a has very good value but the cellular radio downgrade is a big one which people may care about more than they realize due to how it impacts battery life when using 5G.