Oddly enough I was able to beat this quest this time with 4-star classic heroes whereas previously I had to resort to my 5-star bench for healing. At least one maxed Cyprian is now a necessity for any bench to complete this quest. I remember under v19 trying to beat this quest with 2 Joons, Drake, Aegir (pre-buff) and Tarlak. Oddly enough that did not work. Yellow on yellow tile damage did not do enough damage before the bosses were able to fire and my healers weren’t able to keep up.
Now that I have a maxed Cyprian I can just barely beat the quest using 2 Sonyas, Cyprian, Li Xiu and Wu Kong. Not sure if this will be repeatable because there was a point I really needed Sonya to hit the target while under the influence of the traitor.