User blog comment:Calvincambridge30/Versus/@comment-27006668-20151021135759/@comment-26992577-20151021195518

It was never really mentioned how much power Cain could receive from The Darkness through the mark, what we saw is how effortlessly Dean defeated Castiel, even if Castiel tried not to hurt Dean, he failed to get him under control. Cain was much much stronger than Dean, so yes, Cain could kill a seraph without effort and I think he is able to smite Gabriel or Raphael.