It doesn't defeat the purpose, GrapheneOS doesn't protect you from your cell-service provider really.
Discussion
Silent link looks like a great option when traveling if you don't have Projectfi.
True, it's seperate vectors. But in a similar direction.
If google is your cell provider it can geolocate you.
There's no benefit for me in terms of privacy from Google either way.
If I want a more private experience I have to go silent.link
If the IMEI on my hardware is attached to my identity I'm still pwned in terms of geolocation.
So id have to find a pixel for cash at that point, & never use it at my house to be sure.