Fated Duel sounds really cool...but perhaps a bit troubling on the narrative front. Just from this, it feels like the thematic punch behind it (which will no doubt be all kinds of awesome at first) will diminish the more it's used.
I can already imagine a scenario where the PCs are supposed to be impressed and invigorated in seeing their Guardian go toe-to-toe with a baddie, but the actual players could care less because this is about the 20th time it's happened.
I have a similar concern.