That's what I'm talking about. The power has to come from somewhere. Something powerful enough to let a mortal bring down a Dragon has to come from something extremely powerful.
If all you need is to spend 3 refresh to be able to bypass every single defense in the game without consequence, restriction, or anything limiting its use beyond spending one fate point, then I ask you, why would anyone ever not take the power?
I like the latter point, I use it often to demonstrate that something is undercosted or unbalanced.
Which is what you've demonstrated here. (As stated before, the power needs to be prevented from being used with massive damage effects.)
But the former point is problematic. You see, what constitutes an appropriate justification for a power is not something that should be dictated. It should be left up to the people playing.
Would you allow someone to have ACaEBG with the justification that their attacks were actually aimed at the target's Fate? I would, it sounds cool.
Would you allow someone to have ACaEBG for no clear reason, with the source of the character's abilities intentionally mysterious? I would, it'd be a good plot hook.
But you don't have to allow those things if you don't want to.
This subjectivity is a big part of the reason that such things should not be dictated.
Because 3 Refresh is the same cost as Thaumaturgy, or a bunch of cool Social Stunts, or Spirit Form? Not everyone is looking for what it does. It's not even useful to the average "hunter" character because you could get more effective abilities for dealing with lesser horrors for the same Refresh. It only really starts to pull its weight once we're talking Mythic levels of defense. It's a power I expect on dragonslayers, not everyone.
ACaEBG negates mundane armour. That's very useful.
But the basic point is sound. Those 3 points could be spent elsewhere. Possibly better spent, depending on character and circumstance.
