I am saying that Bloody Mistress is deliberately designed to work with being copied by Caranthir.I'm being real saying that: Caranthir is who allows abuses happen because he creates duplicates of strong cards. As you said, the problem is the existence of the copies. So... Who should we blame if not who creates it?
The issue is not that Caranthir being able to copy Gold cards is unbalanced, it is gamebreaking if the copy play generates more points than the original (which was somewhat fixed with the change that Bloody Mistress will no longer "Heal" upon transforming).