It's probably just an indefensible view, but I might hazard that we just have no scale to measure Kellhus on. I don't know if what he did killing all those sranc was impressive or not. Can you see the other dunyain smoking, hanging out in shades and black leather jackets, talking about killing one, no two, or maybe three million sranc with just a snap of the fingers if they had the gnosis?
For all we know, when he falls over in Esmi's arms after warping back is just more acting. Pretend vulnerability to better maintain possession of the empress (or deceive someone watching). Really looking forward to some awesome sorcery in UC. One problem with all this blather is that if Kellhus is so powerful he can just crack the world open whenever he likes, then why bother spending 20 years putting the holy war together. I have not a clue. I think many on here have talked about his need for believers in order to ascend to the outside, I can't think of anything better. Thought myself into a corner, I think.
EDIT: breaking up the text