That just seems to depend on what you personally find 'hot'. Like, I agree that Chika is hot, as I'm sure most people who like women would. But the Molly scene you took that screenshot from is really hot as well, and I'd give Molly a very high ranking on the "most physically appealing characters" tier list. Meanwhile, the Dissonance scene you posted did nothing for me (without context at least). It's all in the eye of the beholder and what you like.
I agree that the latter paragraph describes the best sort of eroticism in this game, where it is strongly supported by the character writing and what is happening within the scene in context. The scene where Kirin taunts Sensei about what he did to Molly was very erotic to me despite it being all dialogue. The Nodoka/Haruka scene was far too short, but what it represented for the characters still made the build up to it feel erotic even if the scene itself could have been far more. I don't think adding sex animations or some such to those scenes would have improved them much for me though. For me, the visuals merely set the stage and the writing then has to take over for the scene to be truly good - which basically never happens in this game.
When there isn't some kind of story/character significance to carry the sex scenes, they generally fall flat IMO. They will often just have Sensei describe what happens in a pretty obvious sort of way, to which the girl then responds with pointless dialogue. *Miku takes my cock into her mouth* "Gee, your cock sure is big, Sensei." Yeah, I can see what you're doing in the image. Give me more details. What do you find attractive about her? What arouses you? How does it make you feel to do this? How badly do you want her? How does she taste or smell? What is her response?
For someone who is so obsessed with sex, Sensei really doesn't seem to get all that into it. He usually treats these girls as onaholes (and not in some kinky fetish sense) and seems exclusively concerned with simply reaching orgasm. Like, he barely seems to notice or care who he is fucking a lot of the time. Despite having a very specific preference for a particular sort of girl, he doesn't even show that much of a response to being able to successfully pick this forbidden fruit compared to when he is with his adult partners, even though the price for fucking these girls is that it could destroy his life at any moment. I guess that fits his extremely detached personality, but it makes for very lukewarm scenes. I would expect that someone like him would feel an all-consuming lust towards these girls, if the urge to fuck all his teenage students is so strong that he goes through with it for real, instead of merely fantasizing about it and having sex with adult women. Instead, he gets distracted by his own internal monologues while fucking them.
I agree, but even then he tends to imply it rather than write it. Like the Nodoka sex scene, where he narrates that Nodoka keeps bringing up her age because it makes Sensei fuck her harder - instead of, you know, actually having Nodoka say that in dialogue and then having Sensei show some kind of emotional response to that which would prompt that behavior. Show emotions and desire instead of telling me about them,
Did Sel say she's 10/10? I wouldn't go that far, but I do like her quite a bit. But then, I can't say I've ever considered how big her butt is in comparison to anyone else, so I guess I'm not much of a butt guy either.