Please feel free to disagree and correct my interpretation...it seems as though this is a matter of semantics and a "lost in translation" concern. That is, when you take the definition from one culture and assume it applies across all cultural perspectives and definitions, you lose something in the process. The idea that NTR is only one thing and we need tags from the Western language, i.e. Cuckolding, Sharing, etc. is more about people not understanding that, in most cases, we are talking about the same thing - "a rose by any other name, blah, blah, blah..."
Maybe I am missing the mark here, I just feel like having a single tag with an extremely open definition leads to the ongoing conflict about what it all means. I posted the following recently in another thread (apparently I overstepped there) and maybe it helps explain my take on NTR. If it helps, great. If not, that is also great.
The 'NTR' tag potentially covers various forms of netorare/netori/netorase and, as such, it can be applied in several ways. (notice there are three separate, yet adjacent terms for NTR ).
Through the actions (or inaction) of the protagonist, or within an agreement with the their partner (wife, fiance, girlfriend), the partner ends up engaging in sexual relations with other people. Typically only the wife/fiance/girlfriend has sex with another (otherwise it is swinging - wherein both partners have sex with different people). Or sharing, wherein the protagonist is willing to have their partner have sex with another as long as they are also involved. Or, swapping, wherein the protagonist will swap their partner, allowing them to have sex with another while they, in turn, are allowed to have sex with the other's partner - yes, it is variation on swinging, although typically reserved for couples swinging together as compared to the swinging where it could be anyone.
In most NTR cases neither partner
wants to cheat, although one or both of them is excited by the prospect of sex with another person - either as the participant or as someone that enjoys watching their partner being pleasured by another (yes, they can be involved depending on which version you are talking about *see above*). This can be something that happens based on an agreement between both partners or it could be where the protagonist convinces the other to have sex with someone for their enjoyment or personal gain, basically 'pimping out' or whoring their partner for their own enjoyment.
Regardless of which form it takes, the partner is having sex with another and both parties may enjoy it or, only one enjoys it.
NTR is the satisfaction of a kink/fetish desire, whereas swinging is a lifestyle, polyamory involves romantic feelings with others over the long term, cheating is completely deceptive and cuckolding is where the partner desires sex with others and the protagonist is powerless to stop it from happening (this CAN be a form of NTR, however it isn't the ONLY form of NTR).
All of that said, I see NTR is a much more complex process than standard cheating or cuckolding, which is why we see all of those tags available for visual novels and games here in the forums. In other words, the NTR tag may apply in addition to or in adjacency to the other commonly used tags (swinging, sharing, swapping, cuckolding, cheating, etc.).
Of course, this will continue to be an ongoing argument and the pro-NTR crowd will demand their NTR and the Harem crowd will scream "they are all MINE!!", while the incest group is just hoping mom and the siblings give it up with their aunt's encouragement and the MILF crowd will only really care if the MC is younger with the "landlady's" booty big enough for 4K full screen...all while the loli folks wonder where the uncensored versions of their VN/game can be found.
At any rate, I am rambling and just wanted to share a definition and take on the NTR thing. (Disclaimer: This is after reading several other definitions of the term and comparing it to what was used in the West).
Because NTR isn't as simple as a lot of people try to make it sound, there will continue to be arguments.