That fight is supposed to be very hard. And its optional, since you dont need to fight it at all.
The biggest difference in difficulty of any encounter is level difference. If you do all other quests in the fort you can do it being on same level or even one level above the Flenser and the monks, which makes it much more doable, although not easy.
And thats great.
If that is still too difficult, you can just get out of the fort through other ways out and then return later with even more levels and better gear.
There is literally no reason why that or other fights should be nerfed, especially not for some theoretical other players who may not win it whenever they want, without putting some effort into it.
