GrapheneOS does not depend on all of the features of pixel phones. The baseline requirements GrapheneOS has are generic, they are not built upon or tied to what pixel phones provide. Pixels actually exceed the baseline rather than barely meeting them.
Other OEMs can make devices that meet the requirements, and Motorola is doing just that. We should get Motorola devices with official GrapheneOS support next year.
https://grapheneos.org/faq#future-devices