About the comparison Vanilla sex scenes vs NTR sex scenes, there's no make sense such thing, because it's a genre issue. Vanilla side is more about romance and caring, it results in a more gentle sex, unless the main theme will be corruption, where it prone to the kinky side, but usually not too intense, because there are no rivals to compete, it's just MC having fun and it limits the possibilities, because there's no another male involved, even a simple sharing to create an M/M/F scene is called NTR here.
The NTR sex scenes are created to cause impact on the player/reader, so everything is increased to the extreme and the Devs put effort to create infinite possibilities with different intensities because they have the freedom for that and they can make the scenes really hardcore(like orgy, rape, swing, swap, etc).
Resuming, the players love vanilla scenes are satisfied with more gentle and less intense scenes and if they compare the scenes in both genres and they think the kinky side has better scenes, I'm sorry to tell you(players), but you(players) need to reevaluate your tastes again.
PS.: It's based on my experience with the adult games and Hentai animes, so it's just my observations about the subject.