I like the revelations we're given of the Inchoroi, how they demonstrate the monstrousness of their creators, the Progenitors, who not only made a weapon race that would perpetuate genocide on an interstellar scale, but took the trouble to GIVE THEM SOULS so they could experience and fear Damnation, and use that terror as a goad to engage in more better genociding.  Holy shit.

As characters they perhaps wound up lacking, but on a thematic level they deliver in spades.

I think Kellhus is taller than Cnaiur (who is himself described as pretty tall), but we don't see Kellhus described as especially muscular or strongly built, whereas we get countless descriptions of Cnaiur's incredibly broad shoulders, his bull-like chest, his heavily muscled arms, his "neckbreaking strength", etc.  You've got to figure a guy described like that (who is also described as tall) would have to weigh at the very least 200lbs, probably significantly more.  Considering a man of average strength might be able to hold 30-40lbs at arms length, shoulder height without dropping it or losing his balance, and a man of great strength might be able to handle twice that, but what Kellhus did was downright superhuman.

And I'm OK with that.  Like I said before, it's all part of establishing Kellhus as badass and explicitly superhuman.  He's quick and coordinated enough to snatch arrows from the air.  He's skilled enough to beat up his world's version of Conan the Barbarian.  He's strong enough to dangle said barbarian over a cliff with one hand.  He's persuasive enough to talk almost anybody into anything.  And it all works well within the context of the story.

I interpreted hair as a metaphor for trees/plant life.

But don't the Mutilated show that Kellhus was at least partially right, in thinking that any Dûnyain would join the Consult?

I think that what you are saying, overall, is somewhat true though.  Had Kellhus been more logical toward the end, things were preventable.  However, had he been so hyper-logical, the situation would never have arose.  The Shortest Path really is through the No-God.  The Mutilated realize this.  Kellhus realizes this too, but finds it an unacceptable solution, probably for the reasons you state.

My take is that Kellhus' decision was the result of Ajokli's influence.  As you say, for the Dunyain the Consult are right and the No-God represents the Shortest Path.  But Kellhus states that he's "more" than Dunyain.  What makes him more?  His connection to Ajokli.  And of course, Ajokli is very keen on stopping Resumption...

From the conversation between Kellhus and the Mutilated, it seems the Gods can see him just fine. They just can't see where he stands. I agree that this is the weakest part of my theory, though.

The Mutilated explicitly state that Ajokli HIDES from the gods in the Golden Room.  I'm fairly convinced that while the gods obviously saw and were aware of Kellhus up to him entering Golgotterath, he was utterly invisible to them once he entered it.  That's why Ajokli had to ride along inside a Decapitant.

But here's something to think about. The Consult are not content to just sit in Golgotterath until they die. Which implies that merely being there doesn't completely hide you from the Gods, at least after you've died. So I'm pretty sure Yatwer knows that Kellhus dies in there, even if she can't see the events that immediately surround it.

The concealment offered by Golgotterath seems to be purely in the Inward.  Once you die your soul goes to the Outside, so even the immortal members of the Consult would still be motivated to fire up the No-God.  Wait around long enough and eventually somebody might show up who's powerful enough to kill you, and then off you to go the Pit.  Yatwer would know Kellhus died if his soul turned up in the Pit, but that seems unlikely unless she snaffled it up and is capable of hiding that from Ajokli.  That's plausible, Yatwer IS powerful, but why would she hide the fact she held Kellhus' soul from Ajokli? 

To Yatwer, the only visible souls/agencies involved with Kellhus' death are Sorweel and Esmenet. They both intended death to Kellhus, and Kellhus died in proximity to them, and with no other souls/agencies around that Yatwer could perceive. Hence she intuits (because she cannot reason) that they killed him. She sees the outcome and the intentions, and fills in the missing details of the causal chain in an intuitive and rather dim manner.

I don't see any contradiction between your argument and Yatwer seeing a Skin-Spy killing Kellhus, assuming of course she could see what happened in the Golden Room at all.  To Yatwer, the actions of the Skin Spy Employee of the Month were the culmination of a causal chain that all happened in accordance with her plan.  Sorweel died to place Kelmomas in a position to ultimately be in the Golden Room.  Esmenet actions served a similar function.

I'm on board with Ark still having some degree of capacity, but I think another factor could be the Inverse Fire.  It appears to have the ability to sooth Erratics and bring them back to some semblance of sanity and lucidity, at least temporarily.  Mek essentially says as much in his scene with Kellhus.  So perhaps the Consult simply exposes their Erratics to the Inverse Fire when they need some extra brainpower or flunkies who can function at a higher level than Sranc or Skinspies.

I feel like Damnation is much more fluid than it is made out to be.  I think that Nonman just got lucky about when he died.  He'd normally have been Damned, but a few dozen Ciphrang were busy being trapped in the Inside, Ajokli was in Kellhus, a Topos short circuited the escape route, Resumption was near...take your pick.  I don't think it was a typical outcome, is what I'm trying to say.

As if Earwa and the metaphysics of souls isn't brutal enough, now there's an RNG element in the mix!  You happen to die when a couple of Ciphrang are having their coffee break or dropping the Outside equivalent of a deuce and your soul can make a break for Oblivion.  15 minutes earlier or later and it's an ETERNITY of torment.  Harsh, but strangely appropriate for the setting!