Something that's always struck me about the character is that he seems to be pretty consistent throughout. I'm not sure Kaine the Vizier that Mikhail Shorn met 16 years ago is any different from Kaine the Dark Lord we see today. He's stronger, with more titles, and certainly has established a fierce reputation, but I don't know that he would react to situations any differently than he would have done back then. So there's no peaks and valleys that denote a character arc of progression, or descent. There's no overall shift in personality from events that have happened to him, or things he's done. He's pretty much the same bad dude now as he always has been, you've just maxed out his level.
However, I've always said that Chaos is more like a comic book series than anything else. Villains die and come back. Legacy characters are all over the place. So, while I don't think that there is much of a character arc to speak of, maybe for Chaos you don't actually need one, since as a Big Bad he is still compelling.
And that's just my perception. Maybe you have all of that and I'm just not reading enough.