I agree. The girls sleep with the MC. But are not in a real relation with him or anything.Personally, I wouldn't mind. But I am not aware of NTL media doing NTR stuff at all. In order for it to be NTR, if we applie the real definition of NTR, there would first have to be a relationship from which Diana is taken away. But since there is no relationship at all, it wouldn't even be cheating. But no matter which word we use now. I don't think that's gonna happen. In NTL media games there are usually no other men sexually involved.
So it can never be NTR in this game.
A harem or all girls going for the MC does not automatically mean they do not have the right to sleep with others.
And on top of all that: The MC sleeps with all he can find on the island. If there is an "evil" act going on here it's not NTR. it's Le Lusty Greed.