I personally disagree with that (But perhaps my ability to see it in a more gray way is because I'm not fan of the genre XP), NTR used to be exactly what the words translates to at first, "stealing another's lover", in fact lots of old NTR doujins around included either next to no interaction from the guy getting NTR-ed or things were only revealed to them at the very end. It actually focused on what it was meant to, aka the girls getting stolen and fucked by somebody else. At some point though the genre started 'twisting' more in what's more seen as nowadays, where it seems more people get off more from traumatizing or ruining the NTR-ed dude's life than on the girls themselves, which is where my personal distaste of most of the genre comes from, it seems more and more pages keep being used to detail how much the MC is suffering or for them jacking off to a video of their girls getting stolen than to the actual sexy girl getting it on with the NTR man of the hour.
Terrible writing aside, I kinda like Fujino's take on it, especially in SAO, because while Inoda still harbors retarded nonsensical hate and urges to ruin Kirito's life for no real reason other than his inferiority complex, we actually DO get a lot more focus in Asuna being stolen than in Kirito suffering thanks to him spending most of the game having no idea what's going on, which even with my little interest in the main story I can appreciate. So I'm not really a fan of how people seem to want Fujino to shift focus towards stupid shit like Kirito becoming a vegetable so Inoda can fuck Asuna in his face, it just feels pointless and dumb to me, especially when Fujino could spend time wasted on creating that plot in the first place to actually giving Asuna or the other girls more actual H-scenes XD