Let me disagree with your concept of Argyl. Although he is a demon, he seems rather undemonic. The fact that the Gryphon Heart had no effect on him is already quite telling, as it should create a portal for demons to Shio. In my opinion, Argyl was initially conceived by the writers not as a true demon, but rather as a demonic personality (unless we consider the possibility of his mission being an opportunity for the player to play on the side of Hell). That is, Argyl is not a true follower of Chaos, but only pretends to be one. Then again, we return to the question – who was he originally?

The Gryphon Heart was created by Tieru; perhaps he “tuned” it not so much to “repel” DEMONS AS SUCH into Shio, but to repel demons who are servants and minions of Kha-Beleth. This focus specifically on Kha-Beleth is justified by the fact that the artifact was created during the War of the Five Eras, when Kha-Beleth was at the head of the demons. Argyl is ambitious and does not blindly obey Kha-Beleth; the artifact "short-circuited" and did not work. Tieru is shocked - how could this happen?; he finds Argyl and invites him over, in order to calmly sort everything out, especially since at that moment the demon is interesting to him not only because of his immunity to the GH, but also because of his extraordinary actions. And as a result -> relatively soon, the demonic essence disappears from the guy. As a CONSEQUENCE! You claim that it didn't exist in the first place, and that this is the REASON for what happened to Argyl later, right? Well, let's go through the scenario with Argyl in "Lords of the Horde," maybe it will open our eyes to some additional facts. I haven't played it yet.

And regarding the logic of Chaos creatures, you seem to have gone too far. Even Kha-Beleth (who seems to be the very embodiment of Chaos) acts strictly logically. And all armies of Hell are subject to strict discipline and subordination, otherwise they would attack the enemy wherever and whenever possible, rather than in battle (although, of course, one must adhere to the framework of turn-based strategy). In general, I think Hell is not Chaos. So many writers have broken their pens writing about the struggle between Chaos and Order that it is wrong to equate Hell (Inferno) and Chaos.

I don't remember attributing inconsistency or lack of discipline to demons. If you thought that when I spoke separately about Argyl, I was ascribing these qualities to all demons, then you are mistaken.
Their Goal is to bring Chaos into the outside world, and not just savor it within their own circles (see Inferno in Heroes 5 ). It was not I who equated Hell and Chaos, but the developers. And I see nothing wrong with this situation, because evil (cruelty, deceitfulness, hypocrisy, cowardice, duplicity), in my opinion, originates precisely in Chaos, in the inner chaos of the soul.

But let's get back to Argyl. After meeting with Tieru's illusion, Argyl, despite all his spiritual quests, acts strictly logically. So accusing him of a lack of logic seems like an insult to Argyl. He is purposeful, persistent, resourceful. This doesn't quite match your image of a confused demon acting under the influence of momentary impulses.
P.S. And this is no longer about the game. Greetings to my neighbor. I only noticed the address today. I am from Bishkek myself.

What kind of logic is it - to rush headlong somewhere to a barely familiar elf, putting your life at risk every hour? Doing so because there is no other way out, that by his actions he has made enemies everywhere – among strangers and among his own people, and even forced his beloved woman to consider herself his worst enemy, although he repeatedly saved her life, exacerbating the displeasure of his monarch, who already looked askance at him? And before meeting Tieru - having the opportunity to remove the GH from Nicholas upon killing him, he does not do so, blinded by his inner turmoil, but then rushes into the crypt for the sake of that trinket? An example of logic... It is Railag who is consistent, logical, "harmoniously balanced"... In comparison with Railag, Argyl is like a 17-year-old guy compared to a 30-year-old man:D .
P. S. Central Asian greetings, come visit:)