Yeah I'm afraid this one is very clear Rules as Written, regardless of perceived intent.

There's even precedent to back it up

The point is, it's not that clear. Although it doesn't say you must be making the attack in your auxiliary arc, I believe that's the intent, and FFG generally rule in favour of their intent on how a card is designed. I'm not denying that as written it works in both arcs given the right conditions, but don't be surprised if this gets clarified in the next FAQ to be an auxiliary arc attack only that triggers the ability.

I think if the intent was to allow both arcs, then it would be worded along the lines of:

"When attacking, if the defender is in your auxiliary arc, you may add 1 <crit> result."

Backdraft:

When attacking a ship inside your auxillary firing arc, you may add 1 (crit result)

your revision:

"When attacking, if the defender is in your auxiliary arc, you may add 1 <crit> result."

You need to give ffg a bit more credit. To make the mistake to write inside, when they really meant from is farfetched.

Conversely, they could have written 'when attacking using your auxiliary firing arc, you may add 1 [crit] result' if they'd wanted it to only work out of the buttguns.

The wording is clear, as it stands. You can argue about intent all you want, but there's no ambiguity in what's actually printed on the card.

No worth to be in an FAQ, this is too rare of a possibility that it will never be a game changer. They probably give zero "*****"

Well considering that there is a FAQ entry around the interaction between Fel's Wrath and Coran Horn which has probably never happened ever, the fact that this is something that you might actually be able to engineer with an astute barrel roll certainly makes it potentially worthy of an FAQ.

Having said that its pretty clear that with the current wording you would get the effect from both shots, you only have to be able to see the targeted ship with your aux arc to trigger the effect. It does not say that you have to be shooting FROM your aux arc to get the effect.

Interestingly, the FAQ still counts a situation where Corran blows Fel's Wrath off the board in the End phase, but Corran dies the next turn, as a Draw. And there is no part of the FAQ or Tournament regulations that adjudicates what happens in this Draw scenario. There's no "if the game would end in a Draw, final salvo" line anywhere.