Would Duality working with combo effects be a bad idea?

[Viridiana]

The 966 crit?

Yeah, at 966 crit total, you should be doing 1.6x damage with crits. Really more like 1.59x, I guess. If you want crits that are twice the damage of your non-crits, you would need something like 2,360 crit rating total.

The question is how many AC's would you then be changing to AE?

The answer is zero, because you must always be averaging 2 AC per minute, or Huton will drop off, unless you're in a situation where it makes sense to hardcast Huton during an invuln phase. In a 350 second fight, you're going to have to use Huton about 10 times (assuming about 50s left on pull). If you Duality AC, and get full +duration, that can be two out of your ten times, but you still need to use it 8 more times before the end of the fight. Your next AE will not be Duality AE, but you can move an AE forward to do more in a row. Basically, all you've done is move from Duality AE plus 2x AC to 2x AE plus Duality AC. The effect of this on your potency per second depends entirely on how much crit you have, as this change only effects where the crits can go.

Edit: I did the math, and the current max-crit setup for NIN would make Duality AC + 2x AE less than 18 expected potency above Duality AE + 2x AC. So if you have to sacrifice pretty much anything to set this up, like, say, losing a single dot tick, you're losing potency. And, of course, this assumes that Duality AC would actually give full +60 duration.