I don't think that's a stupid distinction. I mean, that difference means everything. One is a feel good story, the other is a feel bad story. One strengthens their relationship, the other destroys. They both rely on the wife sleeping with another, but the dynamics are quite different. NTS kind of relies on straddling that line of danger in order to be exciting to some extent, so I still think it's productive to discuss where that line lies and when it's going too far, as it can make all the difference.Also to say something veers too far into NTR is kinda stupid considering NTS is quite literally a sub-genre of NTR whether you like it or not. The primary difference being consent from all parties. The game already has choices for humiliating dialogue or not, so you're safe in that regard.
I otherwise agree with what you said. Now that they've talked about things thoroughly and boundaries and trust have been well established, it'll be exciting to see Amelia planning more things herself and surprising the MC.