Kardia probably should have been AOE from the start, with Soteria being 'cancels the AOE effect, and focuses all of the healing on one person, at a loss'. So if you imagine, for example, Kardia is 50p per person, and Soteria makes it focused to be 250p per hit but on one person, you're effectively 'losing' 150p as the price for focusing the healing onto one person

It'd also make Kardia feel different from Embrace, in that Embrace is ST only (and can be 'amped into ST but stronger' with Union), but Kardia is AOE, and can be made ST with a price