Morale 15 is a useless saint bonus when you hit 100 morale

[Legolas Bow of Athena]

It depends on what you consider useless... technically any time you are willbroken in the first round (before skill attack is used), calvins willbreaker only removes 100 of the morale. multiple morale saintings and a high level morale rune could make you all but unbreakable as far as first round goes. I will add though, that if you have already used a skill attack and THEN get willbroken you will go to 0 morale... so this is ONLY the case in first round of attacks.

No. Calvin's willbreaker reduces all morale not just 100. Trust me, morale bonus saint is absolutely worthless other than the first week of the game.