I dunno. It seems to me they should have a higher potency exactly because they don't proc often. To make up for all the times you have bad luck.
And Heartbreak needs to have its cooldown halved. On bard I can use Misery's End on almost every mob in a trash pack, Heartbreak I can only use on the first because it's not even close to being up yet by the time it becomes usable on the rest.
