It seems a bit strange to strawman a group of people (who aren't here to respond) for the sin of... connecting with characters they're supposed to connect with and not being cucks? Obviously the player isn't literally the MC in most games (at least the ones without character creation, which are popular for a reason). In this game the MC has his own backstory, albeit one that's relatively light, which is done on purpose to allow players to immerse themselves in the world through said character. This is especially the case when it comes to most RPGs as you often have significant control over that character's choices and actions, which leads to a shared identity. When done correctly, this allows the player to not only sympathize, but empathize with the character when they experience both hardship and joy, leading to deeper and more impactful stories. Now yes, we're playing porn games which aren't exactly known for their stories, but this sort of player-character connection is ingrained in all of us who have partaken in any form of story-telling entertainment. Nevertheless, having the player's character be on the receiving end of NTR should understandably be at least a bit jarring, especially if the player wasn't aware it was a possibility.
On the other hand, I would agree that having a complete sense of ownership over every single character in a game without exception can be a bit much. I think the NTR is handled very well in this game, as when it does occur it makes sense in the story/world and is done for a reason without any malice towards the MC. You can't exactly expect a priestess for a sex goddess and a goblin from a culture where monogamy is a foreign concept to be chaste maidens who are, have been, and always will be interested only in the MC. Even still, the player is given an option in all (or almost all?) cases where NTR can occur, which seems like the best-case scenario to me.