I'm not saying that Cain can't do it, I'm saying that a psychic assault is going to have both aspects in that there will be a mental component and a physical component. So while Malicant is attacking him psychologically/psychically, there are going to be physical symptoms of it too, like the bleeding.

I think we should be able to find a happy medium between being incapable of achieving what Cain wants to do and Cain shrugging off side effects because he's immortal.