Demons and Devils are rarely played or perceived, IME, as Chaotic Evil vs. Lawful Evil, but, rather, as chaotic EVIL vs. lawful EVIL. Nuance is functionally absent when good and evil exist as an objective reality.
Frankly, this is due to how these entities have been characterized, entirely outside/separately from their alignment. And mostly, it's because these allegedly super-intelligent beings are really quite stupid and fail to learn from their mistakes, repeatedly.
E.g., devils are associated with making contracts, usually that involve signing over one's soul. Except that almost every devil then immediately proceeds to try to cheat the contractee out of as much as they can, while denying the contractee any rights whatsoever that aren't in the contract. They have earned reputations of being liars, cheaters, and thieves--making them no different from Neutral or even Chaotic Evil other than the window-dressing they use to achieve their aims. Further, even among their own kind, such open disdain for truth, correct conduct, and forthright dealing is commonplace. Most devils seek "Klingon promotions" as TVTropes puts it.
My devils, and my demons, aren't stupid, though demons can be easier to manipulate due to their fundamentally impulsive, desire-driven nature. Devils make genuinely
honest contracts, contracts that clients will
want to fulfill and that THEY want fulfilled. And they seem to give away great power at a tiny cost because they're earning power you can't see, can't touch, because it's wrapped up in symbols and hierarchies and cosmic order that is literally outside the perceptions of mortals. A devil, call him Malael, might contract a heroic adventurer to kill, by certain symbolic means, a man who has secretly murdered children and who will never be caught. Of course, it is irrelevant that the reason Malael wants this murderer dead is that the murderer has a contract with a
different devil, and killing the servants of that devil proves Malael's greater status and power. When the business is concluded, it is genuinely so, though any good businessman will tell you that you check in with past clients to see how they're doing from time to time...and to offer your services.
Souls are a crappy consolation prize compared to gaining influence and prestige in Hell. You certainly can use souls, but that's primitive stuff, child's play. The ultimate goal is rather to get more, and more powerful, servants who are beholden to you just as you are beholden to your liege-lord. Sure, you want to replace your liege-lord, but you must do so
correctly, lest you lose all the contracts and obligations others owe to them. Prestige and legitimacy are of paramount importance, and the difference between "real" and "symbolic" victory begins to vanish--words have meaning and names have power, and symbols transform and control.
Demons are, by comparison, simpler folk, but that doesn't make them safe, nor stupid. Ruled by gnawing hungers and thirsts that cannot be slaked, they desire fulfillment
of desire, and thus tend to raise people up quickly...and bring people down hard and fast. Negotiating with a devil is scary because you never truly know how much the other side is winning, even if you ARE truly, sincerely getting everything you wanted. Plying a demon (they aren't generally the "negotiating" type, though exceptions exist) is scary because they are flighty, impulsive, and absolutely ready and willing to pull a Vader "I'm modifying the deal, pray I do not modify it further." Plus, again, they see and feel what mortals can't. They know the deep secrets, the ways that a million small actions, the prayers and sins of mortals, the falling of the leaves, the rising of the sun, children singing a particular song, all wrap together to be and become the continuation of the world. They know that corruption or control are served by certain actions even if no mortal, no matter how smart, could see those connections. It is extraordinarily rare for a human to be better-informed about reality and the effects of future choices than an outsider would be. They simply do not have the same awareness of reality.
So, I want to dive into this a little further. I recognize that many people find the label of “evil” useful (I’m not going to get into big E vs. little E here, I don’t think it’s really relevant to the point). But I struggle to understand why. Maybe you can help me make sense of it.
Let’s look at a more specific example, instead of talking in broad, abstract terms. And let’s use an example that’s less loaded than always-evil races. Let’s say instead we’ve got a villain. Call him Stroud Van Shmarovich. Now, Stroud is clearly a bad guy, who does lots of bad things. He’s a tyrant who rules over the duchy of Blargovia, oppressing its people and menacing one woman in particular - Aileen - who he wants to force to become his bride. And imagine also that he’s a vampire, so he literally feeds on the blood of Blargovians to sustain himself, and he will theoretically rule forever if someone doesn’t kill him. So, the adventurers have to track down a magic spear (cause it’s like a big stake!) and kill him to save Aileen and free Blargovia.
What does it matter whether we describe Stroud as evil or not? Does it change the adventure in any way?
Two responses.
The first is that you have, by the very construction of the example, moved out of the primary domain of usefulness of "evil." The term is, to some extent, inherently an abstraction; by demanding that we never speak in anything but singular, discrete, concrete realities, of course one can argue that "evil" must be useless, because we're not allowed to speak about the places where it is most useful. "Evil," as a label, bundles together a lot of things, in much the same way that "good" does; e.g. if someone says "I'm trying to be a good person," though they are speaking abstractly, that abstraction is still useful, because it signals that this person has realized that some of their past actions are blame-worthy and that they are putting in the work to stop their blame-worthy actions and commit to virtuous ones instead. Likewise, someone saying, "What I did was evil," is not just admitting that they committed some past action, but rather that they have come to understand and accept that they deserve blame and feel guilt and remorse about that action. It is, most certainly, the case that "X person is evil" can only be determined after observing something like "X person coerces others into abusive romantic relationships," "X person tortures prisoners," or "X person kills innocent people for their personal enjoyment." But by that same token, things like "X object has a color resembling the ocean and the sky" or "X object emits a sound like an avalanche or a bomb" must be observed before we can call objects "blue" or "loud," yet these abstractions linked to physically-observable states of behaviors are perfectly acceptable. (And certainly colors are abstractions, otherwise languages wouldn't have so much disagreement about how many of them there are. Categorizing sounds by loudness is more concrete, but still abstracted across many distinct instances with little in common: 100 dB is abstract unless it is represented as some specific pressure wave, and could be a roaring furnace, a concert, or a trumpet right in your ear.)
The second is a bit different, and perhaps overly technical. You mention all these things: feeding on the life-force of others, coercion of weaker people into relationships, relationships that are built on a dramatic power differential. And I mentioned other things, like deriving joy from killing individuals that are unrelated to oneself or one's situation, or intentionally inflicting pain on individuals over whom you have power. But you may notice a common thread in the descriptions I just gave: none of them imply any need for action on anyone else's part. Why should I care that these facts are true? What factor turns these "is" statement into any kind of "ought" statements for me, or indeed for anyone? Obviously if I wish to avoid being coerced etc. then I should avoid this Stroud fellow, but apart from that, the brute fact "is" statements compel nothing from me. Unless, that is, we are including an implicit evaluative judgment. Unless we are saying, "Stroud has done X and Y and Z,
and those things are blame-worthy." Sweeping the evaluative judgment under the rug by simply assuming that we all agree that it is wrong(!) to coerce or to torture or to enjoy the killing of innocents does not in any way mean the evaluative judgment did not happen. And the common thread through all these evaluative judgments is not merely that they are wrong, but that they are of sufficient wrongness that anyone who has the power to prevent these actions from continuing to occur should--even
must--do so. English has a word very specifically for this kind of thing, for actions that are so severely wrong, they must be opposed by any who have the means to do so. That word is "evil."