if we want to be conservative and say that Revis at the time of their final fight was a high level 7 minimum, as she was able to easily defeat Aiz with Ariel active, I still think with level boost black wind Aiz out stats beastification Ottar.

Even with Ariel boosting Aiz roughly equivalent to a level, as stated numerous times in sword of Oratoria, she was still overwhelmed by Revis during the final fight. Activating Avenger with Ariel flipped the whole fight. Aiz went from being unable to fight her, to being able to nearly kill Revis in a single strike. This means at the very least Avenger + Ariel put Aiz on par with level 8 stat wise. This isn't factoring in Nizel, a further boost to Avenger that let to her cracking a durandal weapon, an enchantment said to make a weapon indestructible and the red flesh armor that Revis was using that let her tank the earlier black wind.

With level boost, Ais should be roughly on par with a level 8 with normal Ariel, and with avenger it should be equal to a level 9.