Dragon 13 is magic affinity. None of your champs has a weak affinity against that.
You have Poison (Kael), Healing (Sethallia and "senesta", if this is, like I suggest, Sinesha), Revive (Scyl), Damage (Coldheart). I really don't know why you have problems at this stage. I think it's more a problem of your gear than of your champs. They should be able to beat dragon 13.
/edit: I wrote my post just a few moments before you made you above posting with pictures of your champs. It definetly IS a problem of your gear. Your Scyl, for example, uses a lvl 5 shield and a lvl 4 helmet.