Do you think that stealing food is the same as someone inviting you dinner?
A better analogy would be this: NTR - Someone breaks into your house and jacks off on your food. Sharing - you invite someone into your house to jack off on your food. And that's why a lot of people don't care about any of the "technicalities." Either way, your food is getting another man's cum on it. And if you eat it, then you are in the same place: you ate food that some other guy's cum is all over.
In real life, this is why if you get cheated on and dump the bitch (i.e., you don't "eat the food" in this analogy) then it sucks but you're not a cuckold. You got cucked, but you are not a cuckold. But if you stick with her or worse, enjoy it (that's eating the cum-covered food), then you are at least a cuck, if not a closeted homosexual who needs the involvement of another man to get sexual gratification, with the woman being just a prop for that.
I've answered before, but I'll restate it. They, sharing and NTR, are technically different. In the same way that trap (and to some degree futa) and gay porn are different. Yeah, each is its own fetish, and they display differently, and you can enjoy one and not the others. But the form, function, and underlying parts are all the same. If someone doesn't like gay porn, they aren't going to care that in one the guy getting fucked by their MC is wearing a 'cute dress' and is skinny or if the guy is a hairy beast of a man. They don't like when their MC fucks someone who has a dick.
Or male domination and female domination. It's the same fetish just from a different direction. So, someone who doesn't like domination because of the force and power imbalance or whatever reason, they won't care what direction it is coming from and who is dominating who. So, while they are different, in that you can like one and not the other, they are also the same. For people who like one and not the other, that's fine, the differences matter. In the same way that a guy might say, "I'm more attracted to black girls, but not really into Asians." So he only watches ebony porn, or avoids a game where every chick is Asian, but you'd never say that "black porn games" and "Asian porn games" are different because the 'difference' is superficial and still part of the overall super group of normal porn.
You see this as well in the discussions about bestiality, furries, and monsters, and where the line is. Sometimes it's easy: dog bangs a chick, it's bestiality, but what about a minotaur, an ape? Also, if the AVN this hypothetical bestiality is in isn't a female MC game or the dog isn't the MC, then is the chick fucking a dog NTR or sharing? Or something else? In a game, if it is another guy fucking your girl it is NTR or sharing, but if it is a dog, what is it? Because I've seen NTR fans lose their shit when a girl in the game fucked an animal, but fundamentally, isn't it "the same," because the girl is getting fucked by not the MC?
Obviously, I'm aware of why bestiality and NTR/NTS are different, and much more different than the differences between NTR and NTS, but the point I am making is one of degrees of differences. As a final example, consider a black MC game and a white MC game. If everything else about the games was the same and the only difference was the MC's melanin levels, that one difference, to a person who cares about it makes all the difference in their enjoyment and engagement with the whole thing. I would say, "Who cares if the MC is white or black, everything else is the same?" The problem in practice is, of course, that most black MC games use a black MC because they are invoking the BBC fetish or race play, but think of a game like Being Super (I haven't played in a long time so this might be out of date information) where you can pick the MC's color between black and white. Is there a real, substantive difference between a black MC and a white MC other than visual preference? If one game has a black MC modeled after Shaquille O'Neal and another game had an MC modeled off Kevin Hart, that would be a more substantive difference than if two identical models were used in two games and the only difference was the skin material used in the Daz renders, but for some people, that single difference makes all the difference.
Also, consider how during all of this talk (the several pages of the discussion), the woman's willingness is rarely mentioned, which goes to my earlier point that in both of these fetishes the female involved is often just a prop. Because if she is willing, then it undercuts the alleged emotions and control involved. You aren't sharing her, nor is she being stolen, because she isn't 'yours' really, she is 'ours.' And if she is unwilling, then the MC is forcing her to be raped if it is NTS, and the real fetish is rape (even if blackmail or some 'less violent' method is employed) and powerlessness and not the actual sex act. So, willing vs unwilling NTR, or willing vs unwilling NTS, from the female perspective are also 'different,' but is it a substantive enough difference that we really need to care that much and have different tags and arguments about it? Or, can we acknowledge that while, yeah technically they are different, they are the same?
Therefore, to finish out and fully bring it back to the topic of NTR and NTS and if they are 'the same' or not, I'll finish with what I started with. Either way, particularly when it is shown on screen and the MC stays with the chick, then they are the same because you still watched your girl get fucked by another dude and you still get sloppy seconds. Another guy came in your food, and you ate it. So for the person who enjoys eating cum-filled food, asking for it or having it forced on you can make all the difference. But in reality and practice, they are the same to most people.
EDIT: TL;DR - How granular do we need to be? At what point do we say, "In the broader discussions and goal of talking about AVNs and fetishes, these are the same despite the minor difference that some have with them," because we can break almost any fetishes down to such a level that it becomes impossible to have real discussions about them if we aren't willing to be honest about when fetishes are fundamentally the same.