First of all, that is very well put into words. But you are confusing netorare and netori here. It's the other way around. You didn't cite a good source. Next you put too little value on the meaning of "stealing". It is this that makes the difference between NTR and simple cheating. Only when a partner is actually really being stolen from a relationship it´s the real NTR. Netorase didn't slide as an NTR for us because we have the word cuckold for it. In the Far East there is no separate word for it, so it is called NTR, although it has a completely different meaning. Only netorare and netori count as NTR, since it is essentially one and the same, only the culpit-victim perspective is different.
But that all doesn't matter at all, because this forum uses a much simpler, crude definition of NTR, which has nothing to do with the true definition of NTR. That is one of the main reasons why there is a NTR dispute in this forum at all.