The reason it follows NTR progression is the corruption arc that is implied when the mother changes to the worse throughout the story. It's no different than a lover getting corrupted and talking shit about her previous bf. Instead of losing a lover, the guy lost his caring mother. I don't know why you emphasize loss, and even support losing a dog as NTR lol, but don't extend it to losing a familial bond without sexual undertones.That is another way of saying 'loss' which was my point. Anyways really admirable attempt but...
That character doesn't exist. Really can't exist. It's a contradiction.
"Mother who loves and cares for her son abandons and abuses her son".
What you end up with is a kid that just doesn't have a relationship with either of his parents, cause he hates them. That's sadly not super rare, and I don't think its NTR as in no way is it sexual. The kid isn't fapping listening to his mom getting banged, he is GONE at his friends house asking to be adopted away from his abusive house. Not even is he longing for a relationship, these people are absolutely happy with just not having their parents in their lives because they know they are toxic.
Now, the reason that your post could kinda sorta pass as an NTR scenario is because WE the player / reader of the work are projecting sexuality onto the mom, even if the protagonist in game isn't.
Which I think steers us near to a 'ludo narrative dissonance' conversation which is way too deep for porn games. I guess to not be too fancy I'd say it'd make for a poor NTR game/story as the character won't align with the player / reader of the work. And we got a lot of those. I was just playing a game linked in this thread, and the NTR is fucking awful its like 'oh hey random green hair chick i've literally never seen before sucking a cock' 'oh hey that random green hair chick is now banging some dude' its technically NTR but it's weak as hell.
"A mother who loves and cares for her son, over the course of the story, turns into a mind broken NTR heroine due to abusive father's training and abandons son at the end." That's the story I was getting at. How is that any different from the standard mother NTR scenario, except the antagonist is the father here?
Bringing up realism is pointless in NTR since the often tropey implementation of the fetish is intentionally unrealistic and extremely cynical in it's view of women and relationships.