In calamity, it covers more of how epic weaknesses work, and why that wouldn't work.
There is an epic in the first book discussed who could only be killed if it was by 5 people at once. I doubt their biggest fear was 5 people attacking them, no more, no less. Epic weaknesses don't work like that. If that was the case, it would be more obvious, and you would have dozens of epics with the same weaknesses, Heights, bugs, the dark, burning to death, violence, blood, needless, that sort of thing.