The Google Pixel requirement also makes me sad. I understand that they have solid reasons why. The problem is Google is incapable of selling their phones worldwide. It's really embarrassing for Google and unfortunate for me.
GrapheneOS can attest to the device's security. The question is whether the app developers will trust such an attestation. Will they put money, time and effort into evaluating and trusting GrapheneOS? Of course not. They will just decide to trust nobody except Google and Apple.
This is the future. We'll be discriminated against. Can't even log into an account from an "unauthorized device". Their servers will just refuse to talk to our phones if they can't cryptographically verify that we have not "tampered with" them. We'll be refused service straight up unless our computers are straight up owned by corporations.
This so called "integrity checking" is meant to protect the corporations from us, not the other way around. It's so we can't do things like hack our way around their "policies".
We also expect Google's Play Integrity API to inevitably be ruled as anti-competitive, which it is.