they always modify her body but they never do it extreme enough to leave her useless as a blob of sex. It bugs me, are the villains playing a cat and mouse game!? Do they only want to make her slightly inflated and increased sensitivity. Why only do Hyper on sakura!?
If Taimanin Asagi 2's translation is accurate, their level of modification is actually the same between Sakura and Asagi, the difference is in their training/experience so Asagi and still control herself a bit better.
In TA3, Asagi breaking is a better outcome for the villains than Asagi being reduced to a blob of sex. It's somewhat hinted in 2, but in 2 it's more or less an unexplored plot point rather than a useful hint.
Edit: wouldn't look too heavily into it though, unlike some visual novels (To Heart, Tokimeki Memorial, School Days, etc.) where there's enough of a storyline that non-h versions can be released without much detriment, Black Lilith's writing in terms of background leaves a lot to be desired.