That's very false. GrapheneOS is primarily a privacy OS that also focuses on security to provide strong privacy.
Sandboxed Google Play has no privileged permissions, which means that those apps have the same permissions as any other apps you can install on Android, meaning the same restrictions.
All that plus the fact that Sandboxed Google Play is a better approach because it offers better app compatibility and is more secure. microG doesn't meet the project's standards.
GrapheneOS will have extreme difficulty being taken seriously while they are "you need to buy Google hardware to run this" project. This is why GrapheneOS has a tiny userbase.