Every warlock talking about this questline has spoken about how devilishly hard it becomes, how incredibly unforgiving the last boss is, and discussed whether it actually needs a nerf before going to live servers. At the time of writing, I only know of one warlock who has completed it.
But after all that work, what if green fire wasn't as great as you thought? Despite all your hard work, what if you decide that your incinerates just aren't fiery enough? It's often said that it's not easy being green, so what if you want out?