Your approach is based on a misunderstanding of what NTR would be for someone who loves Ann.
I understand your point, but think that for someone who loves Ann does not care about your example of the scene or the one that is already done in the game, the NTR will be just as "painful" for them either in one way or another. The thing is that the path is obviously corruption, I think I make it clear that yes, that we agree on that, the thing is that for someone who really likes Ann, that path IN ADDITION to being to corrupt her, will be NTR for THEM , It is the same as for me to see Vanessa fuck with others other than the MC, although I KNOW that she is the standard whore of the game, that does not imply that for me NTR is what I would feel when seeing her with other boys.
You may or may not agree with this, of course, but on the subject of feelings it is difficult to try to create a basis for everyone, since we do not all see it in the same way, and of course we do not feel it in the same way or to the same degree.
For example, there are many people who believe that NTR is only NTR when the MC has real feelings for the character in question, a really important bond, while for others the simple fact that another character in the game approaches a girl who is created for the MC is NTR, for me both options are valid (and I am more in favor of the second because I am very empathetic)