The issue isn't that GPLv3 applies to non-derivative OS components but rather that the terms apply to the overall redistribution of the OS. Including any GPLv3 component means GrapheneOS cannot be used in products where AOSP can be used due to having additional restrictions beyond GPLv2. We don't want more restrictive licensing than AOSP. We're fine with using additional GPLv2 code as long as we're sure it's not going to move to GPLv3 or that if it does we're prepared to maintain it ourselves.