Technically the security works, just for their threat model. An exploit would need root and root means you likely cannot pass attestation AFAIK. The fact that this same exploiter can download all your contacts photos and texts is immaterial to, say, Disney, who want attestation only to prevent ripping of their content.
Security, but not for you, is no security.
No it doesnt actually work because its possible to do privilege escalaction without tampering with firmware or filesystem or triggering other markera. OS will be practically rooted while passing attestation just fine.
Only things attestation do is security theater and messing up people ability to use software of their choosing.