Big Bang Is In the Air

No it hasn't. I made my F/P at the end of July and starting misting O1 at level 90. I was missing with Fire Arrow quite often, but Poison Mist still brought monsters down to 1 HP every time.

I haven't been able to test it myself but I heard reports of people using poison mist at skeles at level 80 and sometimes they would go through the mist unscathed.

You have to take into account that mist still tries to poison every second so a small chance to miss wouldn't make much difference.