My apologies, didn't want to aggravate you. But it really is that simple. Maybe you just did get a really bad RNG. I died once in these cave, because I didn't know the trick.

Now I know it, no problem. When I see a cultist and the telltales of them starting to cast, I step aside. Simple as that. And no longer a problem. And I really did that in regular iron gear.

Edit: I now remember that you are playing in super hard iron man mode. That is of course tough luck, but your own decision. I just do naked corpse runs. :P