Within the context of the comic, I would say the reason why Kai'Sa fails as a horrific figure is because of the framing of the comic and the perspective. The writer keeps telling us she's feared, but the artist frames her as an action hero, and is constantly emphasizing her humanity. Specifically, using the panel you posted as an example, the main framing both claims her as a hero, and a smaller frame emphasizes not only her humanity but compassion - an emotion you don't attach to a horror figure. Her central figure, which is highly emphasized since it cuts across the whole page puts her at an elevated position of power (that we the readers share, which I'll get back to in a moment), also frames her as a hero as it takes her suit (which constantly fails to portray itself as the parasite it is, but that's an overall design flaw that deserves its own post) and has the weaponry mimic the shape of a cape. She echos a figure like Superman, above human, looking down with the intention of using her superhuman status to help others. We know she intends to help because the portrait shot of her literally screams compassion, and uses a warm lighting to further highlight this emotion. Not to mention nothing grotesque is in the portrait, so it's literally just Kaisa not Kai'Sa we see in that frame.
The whole perspective of the comic is flawed towards realizing a story that conveys that she's feared by those around her. We're told that; however, this comic fails to show that. We only ever experience the plot through Kai'Sa's perspective. Sure, the comics third person, the if you pictured our view as a camera filming this, we're almost constantly beside Kai'Sa, and often looking over her shoulder (like in this panel). So, we don't have a reason to fear her. We share her perspective, and so we're sharing/experiencing her power, and her sense of comfort as this is a situation she knows how to deal with, and doesn't expect to experience any personal harm in.
Also, because we're never sharing our narrative point of view of the man, we have to work extremely hard to emphasize with him. We're constantly observing, to an extent even studying, him along side Kai'Sa, and this again, encourages a sense of comfort in the reader. We're not encouraged to worry about what's about to happen. Kai'Sa's expecting him to constantly reject her and for him to die as a result, and it's not surprising when that happens. We expect him to die, which further dissuades from the reader emphasizing with him.
Mostly importantly, because the reader never shares a narrative space with the man, the reader never has a reason to experience fear. Ultimately, Kai'Sa's not supposed to be a horror-villain, but this comic is fighting with itself, trying to exemplify the reactions others have to her, while constantly trying to reaffirm that she's human to the reader. One is going to win over the other, and so the horror aspect of her character fails to be conveyed. Perspective really plays into this. It's why so many horror games are now first person, or fixed upon one character, and that character is never the monstrous figure. If they had genuinely wanted to convey that Kai'Sa can be monstrous and horrifying from an outsider's perspective, they needed to actually give us a outsider's perspective.
feared by enemies of Noxus as a kill-happy assassin.
a dangerous terrorist that hates humans.
hot and actually a decent human being, but still a heretic and that's bad
in Noxian eyes - the undead Blade-Witch who mutilated their Grand General
