I don't want to get into this too much, but in Abrahamic religions sin and the death of the soul are intrinsically connected.
The bit about demons losing their souls in the CoC games is emblematic of demons losing most of the facilities that make them human. While not explicitly said, It's implied that demons lose their compassion, empathy, and morality. From what I understand, demons were not created from lust, but a combination of magic that actively destroyed their souls and rampant hedonism. I wouldn't say that Marae (and subsequently the Gods of Savarra) are the antithesis of lustfulness, because there are many characters within the game that have rampant lust, but are still seen as good and pure. It is more true to say that Marae is the antithesis of soul corruption and demonhood; opposing corruption is what she is known to do by the pure races.
I think it's unfair to compare succubi in this game to succubi in modern mythology. Within modern mythology, succubi are seen as creatures that sustain themselves off sexual energy; where Abrahamic religions correlate lustfulness with sin, and sin with death you can see why such a creature would be portrayed in a negative light. Within Mareth, succubi subsist on the corruption of pure souls, where souls hold the essence of one's humanity. Whether or not you see lustfulness as bad or good, succubi in Mareth and Savarra could still be considered evil as they take away mental facilities like empathy and compassion.
When you talk about the portrayal of succubi in other games, their evilness likely plays off the aforementioned preconception that sinfulness signifies the death of the soul. I've never played Diablo or Dragon Age, but I assume the succubi are seen as demonic man-eaters that corrupt the good men with their tits (and magic). This is more in line with modern mythology. The Witcher subverts these tropes by suggesting that the "evil" monsters were just regular creatures trying to live out normal lives not dissimilar to humans; succubi are not seen as monsters (by the audience), because a witcher does not see lustfulness and magic as intrinsically sinful or evil.
Thank you for the apt description of the reasoning and lore behind demons represented within the game, it helps clarify a lot for me. I personally wouldn't mind more discussion, or a source I could read, in regards to sin and the death of the soul in Abrahamic religion, and what a soul actually is in the context of the game; perhaps it is just a shorthand for the magical influence on brain chemistry?
But if said removal of empathy and compassion is true to demons, I have to wonder how people such as Kasyrra and Vapula exist (Vapula to a lesser extent).
My questioning and criticism is, like you said, much more based on modern mythology, which I find exceptionally strange. I love the aesthetic design and character attributes commonly associated with succubi, but have a distaste for the supposedly inherent immorality and murder. I am strongly interested in seeing media portray sexuality and sexually "objectifying" portrayals in a much more fleshed out and multifaceted light, rather than merely censoring or ignoring sexuality, insinuating that aesthetic beauty is immoral by its absence.
You are correct in regards to Diablo, however, Lilith was (and hopefully still can be) portrayed in a more positive light that was somewhat ruined by Diablo 3 and extended material. Essentially angels in Diablo mythos are shown to be very capable of immoral and flawed behaviour; most demons and angels lack free will, and fight each other due to their intrinsic nature.
Lilith and an angel Inarius are shown to want to escape the endless cycle of death, and make a life of their own; they are the parents of humanity, and Lilith is said to care deeply about her children. The Diablo 3 codex ruins Lilith's interesting aspects as described in the post I linked, but it is still possible they could rectify that in 4.
Lilith is said to be "the queen" and creator of the succubi, which is why I find the concept of the succubi themselves being inherently evil bizarre, as the established lore juxtaposes that.
In Dragon Age, spirits (and demons) are metaphysical beings that exist in The Fade, a plane of existence directly connected with reality, that can be traveled to via magic, dreams, and crossing the barrier called The Veil. Spirits almost all represent specific emotions, and whilst they have free will, they can be readily influenced and corrupted by humans they encounter into negative emotions as demons (or by their own volition, as they have the autonomy to be evil).
Desire demons are always portrayed as succubi esque figures, until Inquisition where they are omitted almost entirely, disappointingly. They are supposed to represent human desire, and have an instinctual drive to use it to their own ends, but my issue is that there isn't a spirit which represents the other aspects of sexuality or love.
I would like to see more modern media reflect on these aspects instead of imitating historical assumptions of sin and puritanism, whilst also avoiding censorship and omitting sexuality entirely. I am very curious to see if Kasyrra will flesh out the actual nature of demons and show that it isn't so black and white.
Separately, I would love the ability to acquire the succubi aesthetic without the inherent notion of evilness, but I haven't tried 2 yet, so that might already be present.