Reminds me of that one case a few weeks back where Graphene wasn't allowed to release a patch because Google wasn't planning on releasing a patch for it for a few more months.

GrapheneOS has a security preview release channel that is opt-in but includes patches from these embargoed vulns already. Again, it's opt-in but for those with a higher threat model use-case it's nice to have.

Would this not defeat the purpose of responsible disclosure? As a bad actor I could learn of secret vulnerabilities from this channel.

These patches are available to all vendors who chose not to protect their users yet.

Releasing binary patches is allowed, this is why GOS have added the security preview channel.

You have google to blame. GrapheneOS tried very hard to make sure they have those security patches as google delays publishing the source tree and it's only available to OEMs