The goal is to give you the option to avoid needing to rely on Google's spying or services while not having to compromise on security.
None of these other solutions regularly get included in Celebrite's documentation as being an explicit benchmark of their software's ability to break into phones. And that's almost certainly due to the fact that unless you leverage hardware security features like what GrapheneOS (and stock Android on a Pixel, and iOS on an iPhone) utilises, you have no chance of going against any actual adversaries.
And I'm not just talking about state actors here, even drive-by opportunistic attacks are likelier on a random other phone running some other Android build.
So yeah, you are running Google hardware, that doesn't make you "googled". It's just a sad reflection on the reality of the hardware landscape. If you want the same security as what GrapheneOS offers, you will currently need to use a Pixel.
I'd be curious to see what comes out of their Motorola partnership though.
If I have to give Google a lot of money every 4-6 years to remain "de-googled" then I never was.
When you go with an alternative you lose superior privacy and security offered by GrapheneOS and you just end up leaking more data back to Google and other ad-tech companies than you would otherwise, negating any benefits several times over.
See: Advanced features, degoogling, privacy, security, and updates sections of https://eylenburg.github.io/android_comparison.htm
The real profit comes from their advertising business.
Maybe the phones are even subsidized by the ad business.