Isarnia is slow, frail, but comes with a high attack stat and a skill that deals damage to all with -44% defense to compensate her big problem of staying alive. That and the wizard class makes her a slow and frail but a hard hitter. She needs that -44% to be worth using over the 4* defense droppers.
Kunchen is slow, but:
he has tanky stats with a great healing skill that cleanses
innate resistance to def-
Elemental link reduces damage to Holy weakness for himself and all other dark allies
Manashield from cleric class avoids mana cuts that otherwise prevent his healing skill from firing
I’m not sure why you want him to get a buffed -44% defense ailment, when he already comes with so many other benefits, that Isarnia clearly doesn’t have.
Cause Kiril also has 28% healing and 30% increased attack…man you can’t compare single effects…you need to see the whole picture…taking ALL abilities into account.