It's actually even worse than if the cable weren't there I guess as without that link if the back box were to become live there's a chance it might not make it to the faceplate.
Then again, a live back box going unnoticed for years is also pretty bad.
The screws for the faceplate connect the backbox and faceplate (and are deemed an ok method of earthing the backbox as long as one of the screw points is fixed) so it’s just redundant more than anything.
It's actually even worse than if the cable weren't there I guess as without that link if the back box were to become live there's a chance it might not make it to the faceplate.
Then again, a live back box going unnoticed for years is also pretty bad.