I agree with your perspective on what makes a good story, but that still doesn't change the opinion that "a good NTR game doesn't necessarily need a highly-rated story". Oh, in case you don't disagree with that opinion and I'm just misunderstanding again, please consider the following as a few ramblings to further explain this opinion.
Take
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as an example: this is a simple scene-finding game about the MC, his mother, and his scumbag friend getting trapped on a spaceship. It has no build-up or opening at all; right from the start of the game, we are already in a situation isolated from the other two.
The pacing is also very crude. It never directly shows us any resistance from the mother, but merely the process of her becoming progressively more amused by the friend's "pranks". If you had trouble seeing Nebel's heroine as a "person", then you definitely wouldn't be able to see the mother in this game as a human being at all.
And yet, for me and some others, it's still considered a good game, and I quite enjoyed playing it. Of course, I would never rate it an 8 or higher, but that's because the story isn't the only thing the game needs to improve to achieve a higher score.
Furthermore, look at other games like
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. They certainly don't have good stories either, just enough for us to roleplay. And yet, those games still receive a lot of praise. Maybe not from you, but from the different audience they target. So, it still prove my point.