I imagine that even if it did have multihit skills, Kardia heal triggers are worded and coded in the same way as Holy Spirit/Circle on PLD, where regardless of number of enemies hit, it only gives the heal effect once. Or Carve and Spit, which says it's a 'threefold attack' but only deals one instance of damage (and one instance of MP restore). Tooltips are weird

Regardless, if it were coded in such a way that certain skills trigger multiple blasts of Kardia, that would indeed be interesting. It'd make Soteria more interesting, at least