something I have not understand in "heal"

[tinkthank]

I have two questions about this also.
I am playing my first game with Arco, and chose a PoD, and am sad to see that his afflictions cant be healed -- what an idiot am I!
But my questions are:
1. In another post, a smart person had written that the chances for any unit or commander being healed is a set %-chance, no matter how many units in a province are being attempted to get healed. (That is, if you have 1000 wounded in a province or only 1, all wounded have the same chance of getting healed per priestess.) I had somehow thought that the priestess had limited capacities and the fewer wounded to attend to, the higher the chance that one of the wounded would get healed; but now it seems to make sense to gather them all together in one province. Is that correct?
2. Why would Arco make a super Tart-Factory (the only magic they are lacking is death)?