Good thoughts, Monsieur G. I never noticed that particular parallel you brought up, but I have done a lot of thinking on the Kellhus/Conphas/Cnaiur trifecta, who are all foils of each other in different ways, especially Conphas and Kellhus. I imagine that Conphas exists as a character in large part to serve as another lens through which to view Kellhus (a human lens, albeit a very specific and extraordinary one).
As you say, it allows us to see Kellhus as something wholly different from any other human. But I also think Conphas is supposed to illustrate the critical difference between blind, delusional pride (even if it is somewhat justified), as opposed to the thing Kellhus experiences which we, as readers, associate with pride. But I don't think it really is pride, not truly. Yes, Kellhus believes himself superior to pretty much everyone he encounters, but then again...he kind of is, certainly on an intellectual and physical level anyway. More importantly, I've never really thought that Kellhus believes himself to be truly infallible -- at least not up until the Circumfixion, beyond which all bets are off. More than that, he also feels doubt numerous times, though mostly in regards to whatever higher game his father is playing (which, again, is pretty reasonable). Conphas has momentary pangs of doubt, but they're always overthrown by his blind certainty in his own success even before it has occurred. That's key.
After Kiyuth, Conphas recalls the moment when he felt absolutely certain that his victory was cemented. And in that case, he happened to be correct...but this is interestingly paralleled, just before his death at Shimeh, where he has a momentary doubt of his success and more importantly the loyalty of his men (I'll get to that in a minute), only to regain that signature confidence in the inevitability of his success...which is swiftly followed by him being decapitated by Saubon.
Cnaiur says a few things to Conphas that I think really illuminate how much he is a foil to Kellhus, which I will quote (not verbatim). I believe both happen before Cnaiur sodomizes him (which is yet another example of Conphas' almost hilarious ability to bounce back from ANY failure or degradation -- he rationalizes all criticism against him as being the delusions of fundamentally inferior people, or in the unique case of Cnaiur, as some bizarre, divine sibling rivalry).
Cnaiur's two quotes directed at Conphas that I wanted to mention:
"You make the whole world a mirror to better flatter yourself."
-------------
"You live this life as if it were your second, as if you were assured of its outcome."
(again, probably not verbatim, but close enough)
The first one, I think, is hugely important to understanding the difference between Conphas and Kellhus. For starters, this isn't just Cnaiur throwing shade -- it's actually pretty astute. I mean shit, we have a scene where Conphas rapes some slavegirl holding up a mirror so he can literally fuck himself. If that's not self-flattery, I don't know what it is.
The use of mirrors as imagery and symbolism is important, because Kellhus is also associated with a mirror; one facing outward, reflecting people's souls back unto themselves. There's a lot to unpack here, and I've touched on this before here, so I'll try to keep it brief. But basically, Kellhus is so successful partially because he actually understands the people around him. He knows them better than they know themselves. Thus, he knows how to truly incite raw faith and belief in his people. Kellhus, from pretty early on, understands how crucial the faith of his people is -- more crucial than anything else, perhaps. This is something Conphas never really grasps. He doesn't treat people like fellow humans, he treats them as animals. Because he's so focused on himself, on his own glory and skill and divinity, and most importantly his own self-assurance of Godhood, that he assumes everyone else must see it too. How could they not? But by making the world a mirror, he has blinded himself to everyone else. This, more than anything else I think, is what causes his downfall. It's not enough to believe yourself divine, no matter how sure you are -- other people must also believe with certainty that you are divine.
Now, Kellhus doesn't really treat his followers as fellow humans either, but again, that's because Kellhus is essentially (and judging on his reproductive issues, quite literally) inhuman. At the same time though, Kellhus in my opinion doesn't think of his people as animals or objects the way Conphas does. He uses them of course, often ruthlessly, yet he does so with an understanding of what humanity actually is. He may not be human himself, but he can at least imagine what it's like to be a human. Conphas never even entertains ideas like this, or if he does, it's always from the perspective that he is superior and that his every utterance is some kind of grand gesture of Godly benevolence. This pattern is most evident in how he treats Martemus, his most trusted ally, who ends up switching sides to Kellhus anyway. I wonder why?