I wonder if there isnt meant to be a dungeon in the plains. Remember we have the weirdness of using iron for the linen armor? They might have cut it in the interest of releasing, but it wouldn't seem out of place to me that there would be another delve in the plains that gave you a different sort of metal for linen armor, or perhaps it's the intended source for black metal and they gave it to the mobs as a temporary solution. Undead fulings (tribal by the way) could be kinda scary. Perhaps they were also larger and degenerated to the short ones you encounter now. Yaggluth would be the largest of the original size (perhaps more like the berserkers). I also find some of the structures in the plains to be kind of purposeless. The large henge and the low narrow stone building are prime examples. The stone one kind of seems like it could be a crypt entrance and is definitely not the current fuling build style.